Seeds and Markers for Use in Imaging

ABSTRACT

A contrast marker having a casing and a novel MRI contrast agent comprising metal complexes disposed around, within, or abuting the casing is provided. Such contrast markers may be placed in a strand, with or without a therapy seed, to produce a seeded strand useful for imaging and in connection with brachytherapy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/668,585, filed Jun. 4, 2010, which was the National Stage ofInternational Application No. PCT/US2008/069861, filed Jul. 11, 2008,which claims priority to U.S. Provisional Application No. 60/949,157,filed Jul. 11, 2007. The applications are incorporated by referenceherein in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

None.

REFERENCE TO SEQUENCE LISTING

None.

FIELD OF INVENTION

The present invention relates generally to the magnetic resonanceimaging (MRI) and more specifically, contrast agents and markers andmethods of the same.

BACKGROUND OF THE INVENTION

Magnetic resonance imaging (“MRI”) is the optimal imaging modality forthe prostate and surrounding critical organ structures. However, withMRI, the standard titanium radioactive seeds, strands of seeds, andneedle tracks appear as black holes (negative contrast) and cannot beaccurately localized within the prostate and periprostatic tissue.Without adequate localization of the radioactive seeds, MRI-baseddosimetry is inaccurate, and therefore, MRI is not used in treatmentplanning, treatment delivery, or postimplant treatment qualityevaluation. For example, brachytherapy titanium encapsulated seedsappear as negative contrast as well as any spacers and needle tracks. Inturn, the seeds limit the ability to perform functional imaging of theprostate as the dosimetry cannot be accurate without positiveidentification of the seed.

MRI-CT fusion has been shown to improve postimplant quality assessmentover CT alone, but this combined imaging approach has not beentranslatable to the community setting owing to inadequacies of fusingcaused by imaging with different bladder and rectal filling, prostatevolumetric differences between imaging modalities, and difficultiesfusing the negative contrast of the seeds, strands of seeds, and needletracks with the seeds visualized on CT scan. Crook, J., et al.,Interobserver Variation Inpostimplant Computed Tomography ContouringAffects Quality Assessment of Prostatebrachytherapy, Brachytherapy,2002, 1(2):66-73.

The consequence of the current inadequate ultrasound and CT imaging issubjective dosimetric evaluation and poor quality assurance during andafter brachytherapy. Poor-quality implants are of critical clinicalimportance because they lead to decreased cure rates and increased sideeffects after treatment. Therefore, there is a critical need fornational standardization of prostate brachytherapy dosimetry. Thiseffort may be achieved through the design of seed implants of improveddesign that incorporate high contrast imaging capabilities.

Furthermore, novel MRI pulse sequences and protocols have beeninadequate in identifying all of the implanted radioactive seeds and isnot an adequate replacement of CT for evaluating dosimetry. For example,a recent article by Bloch et al. have proposed the use ofhigh-resolution contrast-enhanced MRI (HR-CEMRI) with an endo-rectalcoil as a complement to a T2-weighted MRI data set for MRI as a singleimaging modality for the postimplant dosimetric evaluation. However, 12%(CEMRI) and 29% (T2-weighted MRI) of the seeds were missing which canlead to large dose uncertainties and should not be tolerated foraccurate clinical dose reporting.

SUMMARY OF THE INVENTION

A contrast marker that includes a casing and a novel contrast agentcomprising transition metal complexes, disposed within the casing isprovided. The contrast markers may be placed in a strand, with orwithout a therapy seed, to produce a seeded strand useful for imagingand in connection with brachytherapy. Also provided is novel methodologyto determine the appropriate range of concentration of the contrastagent so as to modulate the signal intensity as it relates to theactivity of the therapy seed.

Methods of making the novel contrast agent, contrast marker, a therapyseed and the seeded strand are also provided. To make the seeded strand,at least one therapy seed and/or contrast marker is positioned in thebore of the strand. An optional spacer may be included in the seededstrand between markers or therapy seeds or between a marker and atherapy seed. The seeds, strands and contrast markers may also be usedin connection with radioactive tracers.

In other aspects, methods of using the seeded strand by administering toa patient in need thereof the contrast marker, therapy seed, and/orseeded strand and imaging the patient to determine the position of thetherapy seed and facilitating optimized radiation treatment areprovided. Further, methodology for using MRI contrast agents as contrastmarkers and, more generally, as contrast agents/markers of biocompatibledevices (both therapeutic (therapeutic and non-therapeutic) is taughtherein in order to identify the precise location of an implanted devicein vivo to maximize the therapeutic ratio. Both known and novel contrastagents are taught for use in such novel methodologies.

Methods of using magnetic resonance imaging (“MRI”) in the planning,treatment, and post-implant evaluation for brachytherapy for disease invarious organs including prostate, head and neck, breast, lung, brain,GI malignancies, sarcoma and the like are also provided herein. Thesemethods include real-time MRI-guided prostate brachytherapy.

The foregoing has outlined rather broadly the features of the inventionin order that the detailed description of the invention that follows maybe better understood. Additional features and advantages of theinvention will be described hereinafter, which form the subject of theclaims of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The foregoing summary as well as the following detailed description ofthe preferred embodiment of the invention will be better understood whenread in conjunction with the appended drawings. It should be understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown herein.

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawings will be provided by the Patentand Trademark Office upon request and payment of the necessary fee.

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 a shows postimplant axial images of the prostate with ultrasound.

FIG. 1 b shows postimplant axial images of the prostate with CT.

FIG. 1 c show postimplant axial images of the prostate with MRI.

FIG. 2 a shows novel contrast agents (CoCl₂)_(n)(C₂H₅NO₂)_(1-n), wheren=0.8 to 0.95. These contrast agents are sometimes referred to herein as“C4” and “C4 complex.”

FIG. 2 b shows the structure of the contrast agent L-PG-Bz-DTPA-Gd.

FIG. 3 a shows a Co-based contrast agent that has positive contrast in a1.5-T MRI.

FIG. 3 b shows a Gd Hydrogel contrast agent that has a positive contrastin a 1.5-T MRI.

FIG. 4 a shows a canine prostate in phantom with titanium seeds within atitanium seed-glass [Co-based agent]-titanium seed strand.

FIG. 4 b shows a 1.5-T MRI T1 sagittal image of a dog's prostate with acontrast marker.

FIG. 5 shows a cross-sectional view of a contrast marker.

FIG. 6 shows a diagram of a therapy strand having contrast markers andtherapy seeds.

FIG. 7 shows a prostate phantom as a clear acrylic box that houses gelssimulating the prostate and other structures.

FIG. 8 shows an orthographic projections of the MRI-compatible perinealtemplate for MR-guided prostate treatment delivery.

FIG. 9 a shows MR localization of TVT tumor (circled) in canine prostateMR T2-weighted.

FIG. 9 b shows apparent diffusion coefficient maps.

FIG. 9 c shows dynamic contrast enhanced imaging with perfusionweighting.

FIG. 10 a shows MR spectroscopy of canine TVT in prostate.

FIG. 10 b shows regions of increased choline (Cho) metabolism anddecreased citrate metabolism in the region of tumor growth.

FIG. 11 a shows gross pathology of a canine prostate.

FIG. 11 b shows histology stains (H&E) confirming the presence andextent of the TVT and the estimated region of necrosis.

FIG. 12 shows contrast agent mixed or coated with polymer around aradioactive therapy seed.

FIG. 13 shows a contrast agent inside the therapy seed.

FIG. 14 shows the contrast agent mixed or coated with polymer aroundcasing.

FIG. 15 a shows X-ray diffraction patterns of as-synthesized, annealedand precursors, (CoCl₂ and Glycine).

FIG. 15 b shows the SEM image of annealed sample.

FIG. 16 a shows a Fourier Transform Infrared spectroscopy of Co/glycinesample.

FIG. 16 b shows a Raman spectroscopy of the cobalt complex identifiesits unique chemical fingerprint.

FIG. 17 shows a magnetization plot at 300 K of annealed sample.

FIGS. 18 a-18 d depict the temperature dependence of the magnetizationof the annealed □sample and hysteresis loop.

FIG. 19 shows the pH value of aqua solution of various Co/glycine aquasolutions.

FIGS. 20 a-20 e depict the magnetic properties of aqua solution ofCo/glycine compound.

FIG. 21 a depicts a schematic diagram of an Encapsulated Contrast AgentMarker (ECAM), also referred to sometimes as a “contrast marker.”

FIG. 21 b depicts a schematic diagram of an assembled strand with ECAMand titanium seeds.

FIG. 21 c shows a photograph of assembled brachytherapy strand withECAMs and titanium seeds.

FIGS. 22 a-22 d depicts the linearity of R1, R2, R2* as a function ofthe concentration of the C4 complex, also referred to herein as “C4.”

FIG. 23 shows the temporal stability of the T1 response of the C4complex.

FIG. 24 depicts simulated signal versus concentration for T1 and T2weighted clinical sequences showing the relative difference between C4and prostate tissue.

FIG. 25 shows the effect of T2 signal losses at higher TE valuessimulated in FIG. 24 is measured directly in phantom showing how thecontrast changes as a function of concentration.

FIGS. 26 a and 26 b show samples of the contrast agent, C4 in phantomusing high resolution 3D T1-weighted fGRE and T2-weighted FIESTAsequences.

FIG. 27 shows images of prototypical strands containing C4 versuscontrol levels of C4 (0.5% concentration) in phantom using 3DT1-weighted FSPGR imaging at 1.5 T.

FIG. 28 shows representative images from saturation-recovery sequence(upper left), CPMG multi-spin-echo sequence (upper right), andmulti-gradient echo sequence (bottom images) with differentT1-weightings.

FIG. 29 depicts regression of data to relaxation model. The relaxivityof the agent is equal to the slope of the line.

FIG. 30 a depicts a hollow polymer seed with markers spaced in betweenduring the manufacturing of the needle.

FIG. 30 b shows an MRI marker having the contrast agent positionedinside a needle and/or coated outside.

FIGS. 31 a-31 f show a urinary sphincter and MRI provides superiorimaging of this critical structure responsible for urinary continence.It extends within the genitourinary diaphragm to the verumontanum withinthe prostate (a-f). McLaughlin, P. W., et al., Functional Anatomy of theProstate: Implications For Treatment Planning, International Journal ofRadiation Oncology Biology Physics, 2005, 63(2):479-91.

FIGS. 32 a-32 d illustrate the importance of seed placement accuracy.With a 2 mm misplacement of the periurethral implanted seeds medially,200% of the prescribed dose overlaps the intraprostatic urethra (FIGS.32 a and 32 b). With a 2-3 mm misplacement of peripherally loadedimplanted seeds, the prescription isodose line was compromised leadingto poor coverage of the prostate gland.

FIGS. 33 a and 33 b show that the ECAM having the contrast agent, C4 isable to positively identify the titanium (Ti) implanted seeds in an exvivo canine prostate. Frank, S. J., et al., A Novel MRI Marker ForProstate Brachytherapy, International Journal of Radiation OncologyBiology Physics, 2008, 71(1):5-8.

FIG. 34 shows an MRI image of the MRI visible marker by usingbiocompatible Poly(methyl methacrylate), (PMMA) and contrast agent, C4.

FIG. 35 a shows a photograph of the MRI brachytherapy strand, alsoreferred to herein as a seeded strand.

FIG. 35 b shows a magnetic resonance image from MRI brachytherapy strandin phantom.

FIG. 36 shows an MRI image of the ECAM fabricated by using absorptivefiber, Magnevist contrast agent and PMMA/dichloromethane solution.

DETAILED DESCRIPTION

MRI is superior to ultrasound and CT in prostate gland delineation andsurrounding critical organs like the rectum, urethra, and neurovascularstructures. However, to date, individual therapy seeds and other medicaldevices are difficult to locate and/or identify using MRI, because theneedle tracks, spacers, and seeds (particularly titanium seeds) appearas negative contrast. Frank, S. J., et al., A Novel MRI Marker ForProstate Brachytherapy, International Journal of Radiation OncologyBiology Physics, 2008, 71(1):5-8.

Hence, a contrast marker 10 is provided that can be simply a contrastagent 20, or, the contrast marker 10 can be a medical device that has acasing 15 with the contrast agent 20 disposed within the casing 15 asshown in FIGS. 5 and 6. The contrast agent 20, also a type of medicaldevice, is sometimes referred herein to as an “MR contrast agent” or“MRI contrast agent” and is useful alone as a contrast marker 10. Thecontrast agent 20 renders the contrast marker MRI-visible. The contrastmarker 10 permits the accurate identification of an implantedradioactive therapy seed 35 and other medical devices in vivo, andfacilitates the establishment of MRI-based brachytherapy dosimetry forprostate brachytherapy and other brachytherapies.

Alternatively the contrast agent 20 may be placed in the casing 15 thatis not MRI-transparent, though in such markers the contrast agent 20will generally be disposed on the outer surfaces of the casing 15. Inthis arrangement, the contrast agent 20 may be part of a “paint” orincorporated into a polymer matrix. Ideally, the casing 15 material maybe chosen so that there is minimal interference with MRI signaling ofthe contrast agent 20.

Another medical device, a strand 30 is further provided. The strand 20is capable of incorporating at least one contrast marker 10 and/or atleast one therapy seed 35, or the combination of both contrast markers10 and therapy seeds 35, resulting in what is sometimes referred toherein as an seeded strand 30. The seeded strand 30 may be made with apolymeric strand with a strand bore 40 in which said at least onecontrast marker 10 is placed. The seeded strand 30 may also incorporateat least one spacer element 45, separating the contrast marker 10 fromanother contrast marker 10 and/or a therapy seed 35. Similarly, thespacer element 45 may separate therapy seeds 35 from one another. Thespacer element 45 may be any material, including, but not limited to,water, solid titanium seeds, polymers such as polyethylene,polypropylene, polyamides, PTFE, polyester, polyurethanes,polyvinylchloride, PMMA, Polyetheretherketon (PEEK), or otherbiocompatible polymers, or contrast markers 10 and/or therapy seeds 35.The choice of material may be constrained only by the desire to notimpede the quality of the MRI signal of the contrast agent 20. Spacerelements 45 may have dimensions that permit an accurate assignment ofscale in an MRI image. Furthermore, the use of strands 30 that holdcontrast markers 10 may be useful for the MRI assessment ofbrachytherapy strategies prior to the introduction of any radiationtherapy seeds 35. This will be described in more detail below.

Seeded strands 30 may also contain just the contrast agent 20 or justthe radioactive agent alone or within the contrast marker 10 and/or atleast one therapy seed 35, respectively. Seeded strands 30 may contain acombination of therapy seeds 35 and contrast markers 10, or acombination of multiple markers, and/or multiple therapy seeds 35. Aseeded strand 30 may also contain just radioactive agent alone orcontrast agent 20 alone. Further, the seeded strand 30 may include aradioactive agent that may be disposed within a carrier substrate 50,such as the prototypical titanium seeds known in the art. Theradioactive agent may be contained in the therapy seed 35 made with acasing 15 that is polymeric and non-metallic. Hence, the seeded strand30 may be designed such that the strand bore 40 may be filled withcontrast markers 10 only, therapy seeds 35 only or a combination ofboth. In addition, the contrast agent 20 and/or radioactive agent may bepositioned within the strand 30. The seeded strands 30 may be ordered inany fashion deemed appropriate and may be optimized based on MRIassessments on an individualized patient using a planned brachytherapyapproach (vide infra).

The seeded strand 30 may also include spacer elements 45. Spacerelements 45 may include any entity that would separate (i) therapy seeds35 from each other, (ii) therapy seeds 35 from contrast markers 10, and(iii) contrast markers 10 from each other. The spacers may be anymaterial, including water, or biocompatible polymer seeds. The choice ofmaterial for the spacer element 45 may be constrained only by the desireto not impede the quality of the MRI signal of the contrast agent 20.

The use of polyglycolic acid (pga) bioabsorbable synthetic material issuitable for the casing 15 and/or the strand 30. Therapy seeds 35 maycontain radioactive agents such as Iodine-125, Palladium-103,Cesium-131, or Praseodymium-142 and/or contrast agents 20. Using thistype of material, the contrast agent 20 may be visualized with MRI.Commonly used radioisotopes including iodine (I-125) and palladium(Pd-103), seeds may also contain other components such as X-ray imagingdevices. See e.g., US Published Patent Application Number 2004/0109823,paragraphs [0006] and [0007] incorporated herein by reference.

The contrast agent 20 can be solutions with superparamagnetic,paramagnetic, or ferromagnetic properties. Through a modificationprocess of the standard FDA approved brachytherapy strand, mayincorporate MRI visible solutions in order to locate the radioactivetherapy seed 35 within the prostate and periprostatic tissue. The pgasynthetic strand may hold the therapy seeds 35, contrast markers 10and/or MRI visible spacer elements 45 at discrete intervals within thestrand 30. This improves the quality of the implant over individualloading the therapy seeds 35 by permitting the placement of the seeds inthe periprostatic tissue to cover microscopic disease outside thecapsule of the prostate. By placing therapy seeds 35 into the strand 30,migration of the seeds will not occur during the treatment. Fewertherapy seeds 35 and less activity may be used to achieve optimaldosimetry of the brachytherapy implant than loading individual therapyseeds 35.

For example, prostrate cancer patients may be treated with a permanentradioactive brachytherapy seeded strand 30 using 50 to 120 seedsimplanted into the prostate of the patient. MRI is an ideal imagingmodality to visualize the apex, base, and later borders of the prostate.The anterior portion of the rectum and the prostate interface, as wellas the seminal vesicle and base of the prostate interface, are wellvisualized with MRI as well. MRI-guided prostate brachytherapy may beperformed, allowing for optimization of treatment. Following treatment,a MRI-visible seeded strand 30 will help determine the quality of theimplant by verifying that the dosimetry is consistent with the prostatecancer treatment plan.

Advantageously, the MRI visible seed optimizes image guided radiationtherapy with brachytherapy and minimizes the undesirable side-effectscommonly associated with brachytherapy. Certain novel contrast agentsprovided herein have the general composition,(CoCl₂)_(n)(C₂H₅NO₂)_(1-n). (where n=0.8-0.95) and are also referred toas “C4” or the “C4 complex.” By a cobalt chloride complex contrast agent(“C4”), we have developed an encapsulated contrast agent marker (“ECAM”)shows the location of the implanted radioactive seed in vivo using MRI.MRI contrast markers will provide clinicians the tool for a moreaccurate delivery of radiation treatment and is a device that can beused for other therapies such as either high-, low- or pulse-dose rategynecologic, thoracic, intracranial, ocular, sarcoma, head and neck, andgastrointestinal.

MRI

In clinical MRI, the nuclear magnetic resonance signal from waterprotons in living tissue are used to image organs and disease sites,such as tumors, in 3D. The intensity of this MR signal depends on threeimportant intrinsic tissue factors: the proton density, the longitudinalrelaxation time, T₁, and the transverse relaxation time, T₂. Thus,various mathematical techniques have been developed to highlight thedifferences in T₁ or T₂ to obtain good contrast, ie, the difference inappearance of different tissues in an MR image. Otherwise, MR imageswould be fairly featureless since the amount of water does not varysignificantly in the various tissues of in the body. (Balaji Sitharamanand Lon J Wilson Int J. Nanomedicine. 2006 September; 1(3): 291-295).

MRI contrast agents as are used primarily to improve disease detectionby increasing sensitivity and diagnostic confidence. Nearly allcommercial CAs available today are ECF agents that distributeextracellularly and excrete exclusively via the kidney. There areseveral types of MRI CAs including extracellular fluid space (ECF)agents, extended-residence-intravascular agents (blood pool), and tissue(organ)-specific agents.

Contrast agents used in clinical MRI procedures operate by changing theproton nuclear spin relaxation times of water molecules in theirvicinity, enhancing the detected MR signal in tissue (Lauffer 1987;Caravan et al 1999; Merbach et al 2001; Krause and Editors 2002). Thus,the most commonly used clinical contrast agents decrease T₁ relaxationtimes (also referred to as spin-lattice relaxation) of water protons inliving tissue in the vicinity of the paramagnetic contrast agents. Allcontrast agents are paramagnetic (with unpaired electrons) becauseparamagnetic contrast agents generate very large lattice fields(magnetic and nuclear environments with which the protons interactduring T₁ relaxation) in the immediate neighborhood of the contrastagent, which greatly shorten the T₁ of any water molecule thatapproaches the paramagnetic center.

The term “relaxivity” (r₁ for T₁ relaxation) is the determinant forevaluating the efficacy of any MRI contrast agent. The reduction inwater relaxation times is normally linear with concentration the slopebeing known as relaxivity, a magnitude that reveals the net increase thelongitudinal (1/T₁, r₁) or transversal (1/T₂, r₂) relaxation rates ofwater, produced by 1 mM solution of the contrast agent. It is defined asthe change in the relaxation rate of the water protons per molarconcentration of the paramagnetic contrast agent, and is expressed inunits of mM⁻¹ sec⁻¹. Gadolinium contrast agents used in current clinicaluse have a “relaxivity” r₁ ˜4 mM⁻¹ s⁻¹.

The high-spin paramagnetic gadolinium (Gd³⁺) metal ion is the mosteffective T₁ relaxation agent. It has seven unpaired f-electrons, thegreatest number of unpaired electrons exhibited by any atom or ion, alarge magnetic moment (μ²=63μ_(B) ² where μ_(B) is the Bohr Magneton),and a highly symmetrical, slowly relaxing ground state (⁸S-state) whichproduces strong oscillations near the ¹H Larmor frequency, and thus astrong T₁ effect.

Structures of known Gd-based MRI contrast agents include:

The aquated Gd³⁺ ion is toxic, and therefore for medical use, itstoxicity is usually sequestered by chelation with multidentate (linearand macrocyclic) ligands (Lauffer 1987; Caravan et al 1999; Merbach etal 2001). Important increases in relaxivity were favoured by a deeperunderstanding of the theory of paramagnetic relaxation as proposed bySolomon, Bloembergen and Morgan. In general, theory indicated that toincrease relaxivity it became necessary to increase the number of watermolecules in the first coordination sphere of the metal ion (q,hydration number), to decrease its rotational correlation time (τ_(c)),to favor faster water exchange (k_(ex)) on the complex, or a combinationof these circumstances. Despite the impressive progress in the designand synthesis of Gd³⁺ chelates for advanced CA applications, theresulting Gd³⁺ complexes still possess limitations.

The novel cobalt-based MRI contrast agent (C4) with high T1 signal and arelaxivity ratio (r₂/r₁) of approximately 1.2 which makes it a good T1contrast agent that may have less toxicity than Gd based agents becauseCobalt is a natural component of vitamin B12.

Therefore, MRI contrast agents can be used as markers of biocompatibleimplanted devices (both therapeutic and nontherapeutic) in order toidentify the precise location of the implanted device in vivo tomaximize the therapeutic ratio (i.e. radioactive seed to positivelyidentify to the millimeter where the radiation dose is being deposited).Specifically, the MRI contrast agent can identify the implantedradioactive seed and are not limited to the novel C4 agent. As discussedherein, other commonly used contrast agents using the appropriatecalculated concentration necessary for the appropriate T1 relaxationtime to optimize the positive contrast of the implanted radioactive seedor marker next to the seed by using the algorithms set out herein.

T1 is the longitudinal relaxation time. T2 is the transverse relaxationtime. R1 (1/T1) is a relaxation rate. R2 (1/T2) is a relaxation rate. Indetermining correct concentration, what is important is the T1 time(ms). The shorter the T1 the greater the positive contrast between water(which has a higher T1). Here, each contrast agent has its different T2relaxation times as well. If T1 is shortened too much, this may in turn,shorten the T2 too much and result in lost of positive contrast.Therefore, there is a balance between decreasing the T1 and not allowingthe T2 to decrease too much. Hence, each MR imaging protocol can beoptimized to the contrast agent of choice.

In summary, the relaxivity is a characteristic of the agent. Once the T1relaxation times of the C4 agent were determined, the concentration ofthe Gad agents required to achieve similar T1 relaxation times wasdetermined. This concentration was then tested and found to havepositive contrast inside a polymer casing (PEEK, PMMA).

While it is known to use the relaxivity and relaxation rate(1/relaxation time) to come up with appropriate concentration range tooptimize intravenous (IV) contrast agents, this course of action has notbeen used to optimize the contrast difference between an organ ofinterest and its surrounding structures. One reason it has not been donebefore is that the techniques are very different as well as theobjectives. For example, gadolinium and its derivatives have beenprimarily used as an IV contrast agent but now with the methodologyprovided herein, may be used as MRI positive contrast agents asencapsulated markers.

Clearly, what is not known was to identify the appropriate concentrationrange for Gadolinium and its derivatives that gives the similar T1relaxation time and positive contrast as the novel C4 agent. While thisis true for contrast agents like Manganese that follow the Solomon,Bloembergen and Morgan principle, Gadolinium nanotubes do not follow theSolomon, Bloembergen and Morgan principle and further investigation willidentify the optimal concentration range and sequencing protocols. Theconcentration necessary to achieve a positive contrast signal via T1relaxation times for an encapsulated MRI marker in a polymer casing hadnot been adequately defined to date. Similarly, we were able to figureout that you could not place the contrast MRI marker inside a titaniumseed due to the ballooning artifact and loss of signal from thesusceptibility artifact. Therefore, in order to develop an MRI visibleradioactive seed, a polymer radioactive seed with the MRI markeradjacent, inside or around the casing, or a titanium radioactive seedwith the MRI marker adjacent to the seed. must be used.

Moreover, to optimizing concentration of the MR contrast agent, the T1relaxation times of the C4 agent was used and by working backwards, theappropriate concentrations of other positive contrast agents thatgenerate similar T1 relaxation times were identified. Other contrastagents may or may not have as strong positive contrast signal dependingon their inherent properties and T2 relaxation times.

In short, C4 as a positive MR contrast agent was developed. Other agentswere not initially visible to due inappropriate concentrations beingtested (we know that now) As shown by Grimm et al, placing the MRIcontrast agent inside the titanium seed is not possible due to theballooning artifact that obliterates the positive contrast signal. Inorder to identify a titanium seed, the encapsulated MRI marker(ECAM—encapsulated contrast agent marker) must be adjacent to thetitanium seed. In order to identify a polymer seed, the contrast agentcan be adjacent, inside, or encase the polymer seed (as a paste, paint,or solution). Following the MRI characterization of the C4 agent at 1.5T, 3.0 T, and 7 T, we determined the T1 relaxation times of the C4 agentand its inherent relaxivities. Many would consider our relaxivity to betoo low compared to Gadolinium (“Gad”) or other Gad derivatives, meaningthat we would need a greater concentration of the C4 agent to achievesimilar T1 positive contrast. However, an increased concentration is nota problem because the toxicity profile of Cobalt is different fromGadolinium and Cobalt is a natural supplement of Vitamin B12. See,Toxicological Profile for Cobalt, U.S. Department of Health and HumanSciences, Public Health Service, April 2004. By identifying the T1relaxation times, the concentrations of Gad and its derivatives thatwould provide similar T1 relaxation times and tested Magnevist as anencapsulated contrast agent could be determined. This methodologyprovides the foundation for using MRI contrast agent markers for theidentification of implantable objects in vivo, especially atconcentrations considered non-toxic if the contrast agent were to leakfrom the capsule into the surrounding tissues.

Methods of visualizing implanted radioactive seeds under MRI withcontrast agents using: the C4 complex and other contrast agents, apolymer casing, C4 inside the polymer casing, C4 outside a casing, thecontrast agent inside the therapy (radioactive or chemo agent) polymerseed, the contrast agent outside the therapy (radioactive or chemoagent) polymer seed, and the C4 agent (having properties that make it anideal contrast agent with an r2/r1=1.2) are each disclosed herein.

Encapsulating the Contrast Agents with the Casing

As noted above, the contrast agent 20 can be encapsulated with a casing15 to form the contrast marker 10. Contrast markers are also referred toherein as an “encapsulated contrast agent marker” or “ECAM.” Casing 15may be made of glass or one or more polymers such as polyethylene,polypropylene, polyamides, PTFE, polyester, polyurethanes,polyvinylchloride, PMMA, Polyetheretherketon (PEEK), each of which hasbeen reported to be biocompatible. Woo, R. K., et al., Biomaterials:Historical Overview and Current Directions, Nanoscale, In: R. S. GrecoFBPaRLS, ed. CRC Press, 2004, 1-24. Good mechanical properties and highmelting temperature of these polymers make them an excellent choice asconstruction materials for implantable biomedical applications includingprosthetic and dental materials, implants, dressings and extracorporealdevices (each being considered to be a medical device by the US Food &Drug Administration (“FDA”)). Lee, H. B., et al., PolymericBiomaterials, In: J. D. Bronzino B R, ed. The Biomedical EngineeringHandbook—CRC Press, 1995. Overall, polymeric biomaterials displayseveral key advantages. These include ease of manufacturing intoproducts with a wide variety of shapes, reasonable cost, wideavailability, and wide variety of mechanical and physical properties.Shasti, V. P., Non-Degradable Biocompatible Polymers in Medicine: Past,Present and Future, Current Pharmaceutical Biotechnology, 2003,4(5):331-37.

For MRI applications, low electrical conductivity of these types ofpolymers make the capsules transparent for high radio frequency signals.The schematic diagram of the proposed contrast marker 10 is shown inFIG. 5. The polymer tube can be processed to obtain hollow cylinders upto 5.5 mm in length, 0.8 mm in outer diameter (OD), and 0.6 mm in innerdiameter (ID). One polymer tap 25 can be fastened to one of the tubeends. The tap can be locally heated up to 300° C. to secure theconjunction. Selected contrast agents 20 can be injected into thepolymer. A second tap can be fastened to the seed and heated to preventleakage of the contrast agent 20.

Constructed contrast marker 10 prototypes have been evaluated byclinical and research MRI units in both high and low magnetic fields.The relaxivity of the novel contrast agents 20 at various concentrationswere quantified at 1.5 T, 3.0 T, 4.7 T, and 7.0 T as well as theconcentration of agent that will maximize the signal intensity presentin the interstitial space between seeds and/or markers in the strands30, facilitating identification and localization of seeds. Following theSolomon-Bloembergen-Morgan model, the overall relaxation rate (R₁=1/T₁,R₂=1/T₂) of solutions are determined by their native relaxation ratesand the relaxivity (1/mMol/s) and concentration of the contrast agent20. Bloembergen, N., et al., Proton Relaxation Times in ParamagneticSolutions. Effects of Electron Spin Relaxation, The Journal of ChemicalPhysics, 1961, 34(3):842-50; Solomon, I., Relaxation Processes in aSystem of Two Spins, Physics Review, 1955, 99:559-65.

R _(1,post-contrast) =R _(1,native) +r _(1,agent)·ρ_(agent)

R _(2,post-contrast) =R _(2,native) +r _(2,agent)·ρ_(agent)

The contrast agents 20 were put into special NMR tubes, which fixed in abath of relaxed water to minimize the effect of susceptibilitymismatches on the measurements. T1 of the solutions evaluated using asaturation-recovery experiment. T2 and T2* measured using multi-echogradient- and spin-echo sequences. Relaxation versus contrast agent 20concentration data were fit to the above equations in a minimalmean-square error sense using Matlab (The Mathworks, Natick, Mass.).

Seeded Strands

A method of making the seeded strand 30 includes providing a polymerstrand having a strand bore 40 and positioning at least one therapy seed35 and/or contrast marker 10 in the strand bore 40. A typical therapyseed 35 includes a radioactive agent disposed within a carrier substrate50. Additionally, one can position at least one contrast marker 10 inthe strand as well as a spacer element 45 where deemed appropriate.

For integration of contrast markers 10 next to the therapy seeds 35, itis beneficial to use a flexible, biodegradable (polyglycolic acid)brachytherapy strand, such as those that can be purchased fromBrachySciences Inc, Oxford, Conn. The standard strand typically has aninternal diameter of 0.9 mm. This size is suitable for passing thecontrast markers 10 and therapy seeds 35 through the strand bore 40. Byusing a needle having an interior diameter 0.84 mm the seeds can be set.FIG. 6 shows a schematic diagram of a loaded seeded strand with therapyseeds 35 (where titanium is used as the casing 15) and contrast markers10.

As discussed in US Published Patent Application 2004/0109823, paragraphs[0030] through [0049], brachytherapy strands and methods of making aredescribed as follows:

-   -   Brachytherapy strands typically have a size and shape suitable        for passing through the bore of a needle having an interior        diameter of less than about 2.7 millimeters (10 gauge), less        than about 1.4 millimeters (15 gauge), less than about 0.84        millimeters (18 gauge), or less than about 0.56 millimeters (24        gauge). In one version, the strand is shaped into a cylinder        having a diameter of between about 0.5 to 3 millimeters and a        length of 20, 30, 40 centimeters or more.    -   Any appropriate biocompatible material can be used to form the        brachytherapy seeds. Preferred materials include polymeric        materials which are approved by the Food and Drug Administration        for implantation.    -   In the preferred embodiment, the seeds are formed of a        biodegradable material. Examples of suitable materials include        synthetic polymers such as polyhydroxyacids (polylactic acid,        polyglycolic-lactic acid), polyanhydrides        (poly(bis(p-carboxyphenoxy) propane anhydride,        poly(bis(p-carboxy) methane anhydride), copolymer of        poly-carboxyphenoxypropane and sebacic acid); polyorthoesters;        polyhydroxyalkanoates (polyhydroxybutyric acid); and poly        (isobutylcyanoacrylate). Other examples include open cell        polylactic acid; co-polymers of a fatty acid dinner and sebacic        acid; poly(carboxyphenoxy) hexane; poly-1,4-phenylene        dipropionic acid; polyisophthalic acid; polydodecanedioic acid;        poly(glycol-sebacate) (PGS); or other polymers described below.        See, e.g., Biomaterials Engineering and Devices: Human        Applications: Fundamentals and Vascular and Carrier        Applications, Donald L. Wise et al. (eds), Humana Press, 2000;        Biomaterials Science: An Introduction to Materials in Medicine,        Buddy D. Ratner et al. (eds.), Academic Press, 1997; and        Biomaterials and Bioengineering Handbook, Donald L. Wise, Marcel        Dekker, 2000.    -   These polymers can be obtained from sources such as Sigma        Chemical Co., St. Louis, Mo.; Polysciences, Warrenton, Pa.;        Aldrich, Milwaukee, Wis.; Fluka, Ronkonkoma, N.Y.; and BioRad,        Richmond, Calif., or can be synthesized from monomers obtained        from these or other suppliers using standard techniques.    -   In addition to synthetic polymers, natural polymers may also be        used. In the preferred embodiment, the natural polymers are        biodegradable. For example, tissue such as connective tissue        from the walls of blood vessels or extracellular matrix may be        used as a biodegradable carrier for delivery of radiation or        another therapeutic substance. See, for example, U.S. Pat. No.        5,429,634 to Narcisco. Tissue may be autologous, heterologous,        engineered, or otherwise modified so long as it is biocompatible        with the target tissue. A patient may donate his own tissue to        serve as a carrier for the therapeutic substance and/or        radionuclide. Other tissues or natural polymers may serve as the        degradable carrier matrices. For example, polysaccharides such        as starch and dextran, proteins such as collagen, fibrin (Perka,        et al., Tissue Eng. 7:359-361 (2001) and Senderoff, et al., J.        Parenteral Sci. 45:2-6 (1991)), and albumin (see, for example,        U.S. Pat. No. 5,707,644 to Ilum), elastin-like peptides, lipids,        and combinations thereof. These materials can be derived from        any of the sources known to those skilled in the art, including        the patient's own tissues or blood.    -   Seeds or strands can also be made from synthetic or natural        biocompatible non-polymeric and/or inorganic materials, which        are preferably biodegradable. See for example, WO 99/53898        describing bioabsorbable porous silicon seeds and WO 00/50349        describing biodegradable ceramic fibers from silica sols. Other        examples of non-polymeric and/or organic materials include: U.S.        Pat. No. 5,640,705 to Koruga describing radiation-containing        fullerene molecules; WO 02/34959A2 by Yeda Research and        Development Co. Ltd. describing inorganic fullerene-like        nanoparticles or structures; EP 1205437A1 to Osawa describing        nano-size particulate graphite and multi-layer fullerene; U.S.        Pat. No. 5,766,618 to Laurencin describing a        polymeric-hydroxyapatite bone composite; GB 235140A to Asako        Matsushima describing a ceramic composite such as hydroxyapatite        for sustained release; and U.S. Pat. No. 5,762,950 to Antti        Yli-Urpo disclosing a calcium phosphate, e.g. hydroxyapatite,        bioactive ceramic for timed release.    -   In the case of radioactive seeds, it can be left to the        clinician to select from any number of biodegradable carrier        matrices which contain the radionuclide, so long as the        degradation characteristics of the carrier substance are        consistent with the desired absorption profile. This is because        the carrier matrix itself will be sequestered from the        surrounding target tissue along with the radionuclide until the        radionuclide has decayed to an insignificant activity. At that        time or afterwards, the biodegradable layer overlying the        radioactive matrix will be eroded away, thus beginning a similar        process for the now non-radioactive or nearly spent radioactive        carrier.

In addition radioactive tracers may be optionally used as described inUS Published Patent Application 2004/0109823, paragraphs [0040] through[0046] as follows:

-   -   Optionally, brachytherapy seed or strand can be imparted with a        means of tracing the radioactive contents should those contents        be released inadvertently. Unforeseen problems associated with        leakage of radioactive material, whether it be into the        surrounding tissues in a patient, in a pathology lab, in a        nuclear medicine lab, or in the operating room have been        recently discovered as they relate to polymer seeds. The        seed/strand should contain a means of tracing their contents        should those contents be released inadvertently. This mechanism        can rely on inclusion of fluorescent, luminescent, colored,        pigmented or other approaches for tagging, detecting, or        otherwise identifying the seed/strand contents either visually        or with instrument assistance.    -   Fluorescence can be imparted using the appropriate polymer or        other biodegradable substance, such as described by Sung in U.S.        Pat. No. 4,885,254, Bryan in U.S. Pat. No. 6,416,960 B1,        Barbera-Guillem in U.S. Pat. No. 6,548,171 B1, or Greiner in        U.S. patent application Ser. No. 2003/0010508A1.    -   Luminescence can be imparted using the appropriate polymer or        other biodegradable substance, such as described by Towns in WO        01/49768 A2, Sakakibara in EP 1 311 138 A1, Bryan in U.S. Pat.        No. 6,436,682B1, Hancock in U.S. patent application Ser. No.        2003/0134959A1, or Wood in U.S. Pat. No. 6,552,179B1.        Bioluminescence materials are described in U.S. Pat. No.        5,670,356. In addition, chemiluminescent and electroluminescent        substances might be utilized, as well as other types of        luminescent substances as would be known to one skilled in the        art.    -   Quantum dots may also be loaded into the seeds and utilized to        locate spilled substances from ruptured seeds/strands, like        those described in U.S. patent application Ser. No. 2003/0129311        A1 or Dobson in WO 95/13891 (see also Jaiswal et al., Nature        Biotechnology 2003; 21:47-51, and Quantum Dot Corporation's        Qdot™ biotin conjugate).    -   Dyed biodegradable polymeric material may be used, as described        by Burkhard in EP 1 093 824 A2. Other dyes can be used as        indicated. Ultraviolet light can be utilized to detect a        therapeutic agent like radioactive substances or drugs using a        format described by Koshihara in U.S. Pat. No. 6,456,636 B1, or        by Nakashima in WO 00/53659. Infrared dyes may be used, as        described by Paulus in U.S. Pat. No. 5,426,143.    -   Those skilled in the art will be familiar with labeling, doping,        or tagging the contents of the seeds/strands with agents that        can be identified without modification, or pro-agents that can        be identified by the addition of an activating substance or        other means, such as labeled antibodies and the like.

Furthermore, other non-radioactive drugs can be used in combination withthe strands. As described in US Published Patent Application2004/0109823, paragraphs [0047] through [0049],

-   -   [p]olymers can be used to form, or to coat, drug delivery        devices such as strands or strands containing any of a wide        range of therapeutic and diagnostic agents. Any of a wide range        of therapeutic, diagnostic and prophylactic materials can be        incorporated into the strands, including organic compounds,        inorganic compounds, proteins, polysaccharides, and nucleic        acids, such as DNA, using standard techniques.    -   The non-radioactive drug can take the form of stimulating and        growth factors; gene vectors; viral vectors; anti-angiogenesis        agents; cytostatic, cytotoxic, and cytocidal agents;        transforming agents; apoptosis-inducing agents;        radiosensitizers; radioprotectants; hormones; enzymes;        antibiotics; antiviral agents; mitogens; cytokines;        anti-inflammatory agents; immunotoxins; antibodies; or antigens.        For example, the non-radioactive therapeutic can be an        anti-neoplastic agent such as paclitaxel, 5-fluorouracil, or        cisplatin. It can also be a radiosensitizing agent such as        5-fluorouracil, etanidazole, tirapazamine, bromodeoxyuridine        (BUdR) and iododeoxyuridine (IUdR).

Finally, in some aspects, the therapy seed 35 may incorporate contrastagents 20 as described above and shown in FIG. 13. Plastic therapy seeds35 are known in the art and the contrast agent 20 may be incorporatedinto such FDA approved therapy seeds 35. Alternatively, the contrastagent 20 may be coated onto the outer surface of such therapy seeds 35.Thus, MRI-visible therapy seeds 35 are generated by incorporatingcontrast agents 20 allowing for direct detection of a therapy seed 35.

As described above, MRI visible seeded strands 30 by proxy use contrastmarkers 10 placed next to the therapy seeds 35 with a stranding materialso that the therapy seed 35 will be readily identifiable under MRI dueto its proximity to the contrast marker 10. The total length of thecontrast marker 10 can be between 1 mm to 2.0 cm so that the unit of thetherapy seed 35 plus the contrast marker 10 can vary, and the distancebetween consecutive therapy seeds 35 can also vary.

In the approach wherein the contrast agent 20 is part of the therapyseed 35 one can place about 0.3-1 μL of the contrast agent 20 into atypical plastic radioactive seed. No additional contrast marker 10 isrequired. The therapy seed 35 has standard dimensions with a length ofabout 4.5 mm. The therapy seed 35 may be implanted alone or in a seededstrand 30 (i.e. radioactive seed with predetermined spacers) format asdisclosed hereinabove.

In other configurations, therapy seeds 35 may be coated with thecontrast agent 20, or the contrast agent 20 may be incorporated into astranding material (i.e. polyglycolic acid matrix) that is manufacturedto coat the individual therapy seeds 35. About 15 μL of the contrastagent 20 can be used in such a coating process. The coated therapy seed35 may be implanted alone or in combination with additional therapyseeds 35 and spacer element 45 in the seeded strand 30.

The contrast markers 10 and/or therapy seeds 35 may also include acarrier substrate 50 positioned within the casing 15. The carriersubstrate 50 may be made with nanoparticles, or a single bulk materialoccupying a substantial fraction of the void volume of the casing 15.The carrier substrate 50 may be any material that can incorporate aradioactive therapeutic agent for use in radiation therapy. Radioactivetherapeutic agents useful in connection with the subject inventioninclude, but are not limited to, palladium-103, iodine-125, andcesium-131, Praseodymium-142. Also, contrast agents 20 may be absorbedon the surface of the carrier substrate 50. It may be possible toincorporate a radioactive therapeutic agent within the casing 15 itself,possibly obviating the need for the carrier substrate 50, except whereit may be desirable, i.e., as a carrier of the contrast agent 20.

The seeds and markers described herein may be useful in treating avariety of diseases inflicting a variety of organs including heart,abdomen, head and neck, prostrate, pancreas, liver, lung, brain, andbreast, and for gynecological treatments. While the seeds and markersare useful in treating different types of cancers found in these organs,the markers and agents either together or alone maybe useful indiagnostic applications and other therapy applications. For allapplications, where appropriate, the contrast agent can be coated onto adevice, placed in a contrast marker adjacent to the device and/or placedinside a device.

For example, the contrast agent may be coated onto a seed, biopsyneedles or MR-guided monitoring probes of thermal therapies (i.e.laser-induced, RF-induced, and cyromediated procedures) and used in thebrain. Similarly, coronary stents, intravascular, IV catheter, guidewire and balloon catheters may be coated with the contrast agent.Prostrate applications include intraprostatic contrast agent, polymerneedles, polymer catheters, fiducial marker on end of a catheter orneedle, coating speed, coating spacer, fiducial marker next to see andHDR applicators.

For imaging the breast, the contrast agent could be used in connectionwith catheters (HDR, PDR and LDR), balloon catheters (HDR therapy) andas fiducial markers. Likewise, in other gynecological applications, thecontrast agent may be used with tandem HDR applicators, or HDR or CDRcatheter applicators. The contrast agent may also be useful inconnection with an abdomen drain. The contrast agent is also useful ininterventional radiology applications such as balloons, filters, drains,and stents.

Brachytherapy

Brachytherapy, also known as sealed source radiotherapy orendocurietherapy, is a form of radiotherapy where a radioactive sourceis placed inside or next to the area requiring treatment. Brachytherapyis commonly used to treat localized prostate cancer, cancers of thebreast, and cancers of the head and neck.

Prostate brachytherapy is a nonsurgical standard-of-care approach forthe treatment of prostate cancer. Patients who choose prostatebrachytherapy do so because treatment consists of a 1-day outpatientprocedure and cure rates are similar to if not better than those seenwith surgery or external-beam radiation therapy. Butler, W. M., et al.,Introduction to Prostate Brachytherapy, In: B. R. Thomadsen M J R, W. M.Butler, ed. Brachytherapy Physics 2nd Ed, 2005, 538:42. Additionally,patients treated with prostate brachytherapy almost always experience ahigher quality of life, with less incontinence and better erectilefunction, than surgically treated patients. Frank, S. J., et al., AnAssessment of Quality of Life Following Radical Prostatectomy, High-DoseExternal Beam Radiation Therapy, and Brachytherapy Iodine Implantationas Monotherapies for Localized Prostate Cancer, The Journal of Urology2007, 177(6): 2151-2156.

Prostate brachytherapy is sought out by men diagnosed with cancer.Prostate radioactive seed implants, also know as brachytherapy, is astandard of care one-day outpatient treatment for approximately 30% ofthe 210,000 men annually diagnosed with prostate cancer. Outcomesfollowing Brachytherapy are good but can vary significantly depending onthe quality of the implant with an 8 year PSA relapse-free survival of93% vs. 76% for high and low quality implants, respectively. Zelefsky,M. J., et al., Multi-Institutional Analysis of Long-Term Outcome ForStages T1-T2 Prostate Cancer Treated With Permanent Seed Implantation,International Journal of Radiation Oncology, Biology, Physics, 2007,67(2): 327-333.

Hence, outcomes with high-quality prostate brachytherapy implants aregood, but there is substantial heterogeneity between radiationoncologists institutions in the quality of implants. Although prostatebrachytherapy prescription doses are uniform between institutions, thereis significant variability regarding prostate treatment length, planningtreatment volume, seed strength, dose homogeneity, treatment margins,and extracapsular seed placement. Merrick, G. S., et al., Variability ofProstate Brachytherapy Pre-implant Dosimetry: A Multi-institutionalAnalysis, Brachytherapy, 2005, 4(4):241-51. Experts have differentopinions about whether or not to use a preplanning or intraoperativeplanning approach, how to evaluate the implant post-operatively withCT-based dosimetry, and which patients are appropriate candidates forbrachytherapy alone versus a combination of external-beam radiationtherapy plus brachytherapy. Shah, J. N., et al., Improved BiochemicalControl and Clinical Disease-free Survival with Intraoperative VersusPreoperative Preplanning for Transperineal Interstitial PermanentProstate Brachytherapy, Cancer Journal, 2006, 12(4):289-97; Matzkin, H.,et al., Comparison Between Two Iodine-125 Brachytherapy ImplantTechniques: Pre-planning and Intra-Operative by Various DosimetryQuality Indicators, Radiotherapy and Oncology, 2003, 68(3):289-94; Han,B. H., et al., The Effect of Interobserver Differences in Post-implantProstate CT Image Interpretation on Dosimetric Parameters, MedicalPhysics, 2003, 30(6):1096-102; Frank, S. J., et al., InterstitialImplant Alone or in Combination with External Beam Radiation Therapy forIntermediate-Risk Prostate Cancer: A Survey of Practice Patterns in TheUnited States, Brachytherapy, 2007, 6(1):2-8. Owing to the subjectivenature of post-implant quality evaluation with CT-based dosimetry, somecommunity physicians have such difficulty evaluating the quality oftheir implants that they outsource their post-implant dosimetry tocompanies like ProQura in Seattle, Wash. to allow feedback from expertsin the field (Seattle Prostate Institute). Among these physicians whooutsource post-implant dosimetry—and by doing so indicate that they areconcerned about quality and acknowledge the difficulty of post-implantevaluation—up to 25% of implants are found to be of poor quality.Merrick, G. S., et al., Initial Analysis of Pro-Aura: AMulti-institutional Database of Prostate Brachytherapy Dosimetry,Brachytherapy, 2007, 6(1):9-15.

Currently, the location of the titanium radioactive seeds used forprostate brachytherapy with respect to the tumor and normal criticalorgan structures remains ill defined with standard imaging modalitieslike ultrasound and computed tomography (CT) (FIG. 1 a-b). Positivecontrast of the titanium seeds on CT permit accurate localization of theseeds for post-implant dosimetry. However, these standard imagingmodalities, which are used during treatment planning, treatmentdelivery, and post-implant treatment quality evaluation, provideinferior visualization of the prostate and surrounding critical organstructures, which leads to subjective determination of the quality oftreatment.

Urinary incontinence is a major health problem following treatment.Following treatment, men are often embarrassed if they leak urine, wettheir pants, and wear diapers/pads. Recent data reveal that followingbrachytherapy, approximately 15% of men will experience incontinence 2years and longer after their treatment. Sanda, M. G., et al., Quality ofLife and Satisfaction With Outcome Among Prostate-Cancer Survivors, NewEngland Journal of Medicine, 2008, 358(12):1250-61; Frank, S. J., etal., An Assessment of Quality of Life Following Radical Prostatectomy,High-Dose External Beam Radiation Therapy, and Brachytherapy IodineImplantation as Monotherapies For Localized Prostate Cancer, The Journalof Urology, 2007, 177(6); 2151-6. The internal and external urinarysphincter cannot be adequately identified on standard imaging modalities(i.e. ultrasound, CT, or fluoroscopy) currently used for treatment, butthese structures are well visualized on MRI (FIGS. 30 and 31). The useof superior imaging with MRI during the planning, treatment andpost-treatment evaluation will result in improved cure rates and adecrease in complications following brachytherapy.

Increased accuracy of seed placement with MRI will improve outcomes. Thecurrent standard imaging solutions used for brachytherapy are suboptimal(FIG. 30). Frank, S. J., et al., A Novel MRI Marker For ProstateBrachytherapy, International Journal of Radiation Oncology BiologyPhysics, 2008, 71(1):5-8. Optimal imaging with MRI would improve theaccuracy of seed placement thereby maximizing treatment efficacy andminimizing treatment related complications due to unnecessary radiationdose to the urinary sphincters (FIGS. 32 a-32 d).

MRI is the ideal imaging solution, but is currently limited by seedtechnology. MRI is the optimal imaging for the planning, treatment, andpost-implant evaluation for brachytherapy and its efficacy has been welldescribed. Tempany, C. M., et al., MR-Guided Prostate Interventions,Journal of Magnetic Resonance Imaging, 2008, 27:356-367; D'Amico, A. V.,et al., Comparing PSA Outcome After Radical Prostatectomy or MagneticResonance Imaging Guided Partial Prostatic Irradiation in SelectPatients With Clinically Localized Adenocarcinoma of the Prostate,Urology, 2003, 62:1063-1067. However, its use has been limited due tothe inability to accurately identify the implanted radioactive seeds.Roberson, P. L., et al., Use and Uncertainties of Mutual Information ForComputed Tomography/Magnetic Resonance (CT/MR) Registration PostPermanent Implant of the Prostate, Medical Physics, 2005, 32(2):473-82.All implanted seeds in the U.S. have radioactivity encased within aparamagnetic titanium shell. Under MRI, the implanted seeds in theprostate and periprostatic tissue appear as a negative contrast that isnon-distinguishable from needle tracks and implanted seed spacers (FIG.30). Additionally, artifacts generated through selected MR pulsesequencing protocols have not alleviated this problem. Attempts havebeen made to incorporate MRI in the post-implant evaluation throughfusion of post-implant CT. Crook, J., et al., Interobserver Variation inPostimplant Computed Tomography Contouring Affects Quality Assessment ofProstate Brachytherapy, Brachytherapy, 2002, 1(2):66-73. However,differences in prostate gland size based on imaging modality, imageregistration variability due to different imaging tables (hardware) anddifferences in bladder and rectal filling, and excessive cost andinconvenience have decreased enthusiasm for MRI/CT fusion in thepost-implant setting.

MRI-based brachytherapy transforms treatment from an “art” to a“science.” On the surface, the innovation may appear modest, but themethods and devices presented herein are actually a technologicaladvances within brachytherapy with the potential to significantly changethe field by improving the quality of every implant that is performed.In the future, clinicians will have less anxiety about the quality oftreatment delivered and during the MRI evaluation of treatment, if theprostate cancer is inadequately covered, additional seeds can beimplanted to optimize treatment.

A systematic use of MRI brachytherapy provides a clinician the tools toperform consistent high quality implants. The use of MRI with ECAMsimproves cure rates, decrease complications, and is ideal for thedevelopment of national standards for prostate brachytherapy.

For applications in brachytherapy, it can be desirable for the contrastmarker 10 to have similar dimensional sizes to the a typical radioactivetherapy seed 35 known in the art, so that the both contrast marker 10and therapy seed 35 can be placed in a strand 30, creating an seededstrand 30. Due to the limited size of implantable contrast markers 10(the typical dimensions of 5.5 mm in length and 0.8 mm in outer diameter(OD)) the volume of contrast agent 20 inside the contrast marker 10should be less than 1 μL. The contrast agent 20 used as a contrastmarker 10 has the following properties: (i) it should have a strong MRIsignal to minimize damage that might be caused by leakage of thecontrast agent 20; (ii) have a low electrical conductivity to besufficiently transparent to high radio frequency; and (iii) should bebiocompatible with human biochemistry.

MRI-Based Dosimetry Methodology

The following technique is for prostate implants but is not limited tosuch—similar planning, treatment and evaluation can be performed withGYN, Breast, Sarcoma, Lung, Brain, Heart or Kidney procedures using MRI.

Planning

Planning can be performed as “pre-planned” (i.e. prior to the patientarriving in the operating room/procedure room) or “intra-operativeplanning” (i.e. MRI-operative suite). A standard and/or functional MRIis performed at either low field (0.5 T, 1.5 T, 3 T) or high field (4.7T, 7 T) with or without an endo-rectal coil. Various MRI protocols andimaging sequences with and without contrast (i.e. derivatives of T1- andT2-weighted) will be obtained to optimize identification of thetreatment volume and normal organ structures. An ultrasound or CT may beobtained and transferred to the treatment planning system for fusionwith MRI.

The DICOM images are transferred to a treatment planning softwaresystem. Template registration will be performed. The target volume andnormal organ structures (rectum, bladder, penile bulb, urethra,neurovascular bundles, etc.) are contoured. The amount of activity(millicurie) per seed will be defined. The type of radioactivity usedwill be defined (Pd-103, I-125, Cs-131, etc.). The type of seed (vendorspecific) will be defined. The type of material of seed will be defined(either titanium, plastic, glass, etc.) in order to determine where theMRI marker will be set in proximity to the seed to optimizedidentification of the seed. The seed itself may be MRI visible with theMRI marker inside. The ratio of MRI marker(s) to seed will be defined,with either a 1:1 ratio or 2:1 ratio. The distance of the MRI marker(s)to the center of the radioactive seed will be identified and entered.

Either manually or through inverse planning, the seeds with MRI markersare optimized to achieve dosimetric coverage of the target volume whileminimizing dose to the critical organ structures. A dose volumehistogram (DVH) can be obtained by observing the dose to all targets andorgan structures for plan optimization. The amount of activity pertarget volume will then be evaluated to determine that appropriatetreatment will be delivered.

The needle unit and MRI visible seeds/strands will be adequatelysterilized. The needle unit will be loaded with the radioactive seedsand MRI markers as defined by the treatment plan. The needle can be madeof a metal or polymer. The MRI visible radioactive seed can be a singleunit or in a row of seeds attached by strand material. For qualityassurance, prior to loading the MRI visible seeds into the needle unit,MRI imaging may be performed to verify that the MRI marker(s) to seedratio is consistent with the treatment plan. The needle unit loading canbe pre-loaded (i.e. prior to coming to the operating/procedure room) orintra-operatively loaded. If pre-loaded, the packaging should be suchthat there is adequate shielding for distribution. The needle unit mayor may not be MRI compatible. The needle unit should be MRI compatibleif the implant is in an MRI environment.

Treatment

The patient is brought to the operating/procedure room. The patient mayor may not be under anesthesia. Quality assurance procedures areperformed to verify the patient and the treatment, and to verify thatthe treatment plan is consistent with the patient and procedure. Theneedle loading will be verified with the planned MRI marker(s) per seedratio or MRI visible seeds. The perineum of the patient will be preppedand draped in the standard fashion. The patient will have either anendo-rectal MRI coil placed or an ultrasound probe with the templateplaced next to the perineum. It is possible that the patient can havethe implanting of the needles performed via ultrasound and then theneedle(s) location verified with MRI prior to placement of the MRIvisible seeds.

By using MRI in connection with prostate specification methodologies,needles can be implanted in real-time to the desired location as definedby the treatment plan. Real-time implementation provides for all of theneedles to inserted as defined by the treatment plan and the MRI visibleseeds immediately identified upon entry in vivo. The placement of theneedles can be verified with respect to the location of the bladder,rectum, urethra, penile bulb, ejaculatory ducts, seminal vesicles,neurovascular bundles, etc. to prevent trauma to these normal structuresto minimize the risk of morbidity. The MRI DICOM images can beimmediately transferred to the treatment software with identification ofthe MRI markers. The dosimetric evaluation will be performed to optimizethe patients treatment.

Post-Treatment Evaluation

Following the procedure, a standard and/or functional MRI will beperformed at day 0 and/day 30 after the implant. A CT may also beperformed to fuse with the MRI. The DICOM images captured will betransferred to the treatment system and the target volumes and normalorgan structures will be contoured and delineated. The MRI markers willbe manually or automatically identified. The dosimetric lines will beapproximated to the radioactive seed which will have been predeterminedbased on the distance of the MRI marker(s) to the center of theradioactive seed. A dosimetric evaluation will be performed to verifythat the target volume has been adequately treated as defined by thetreatment plan. If the dose to the target volume is inadequate,optimization will be performed with the treatment software to determinethe location of additional seeds with MRI marker(s) required. If seedshave been implanted too close to critical organ structures, an MRIcompatible seed retrieval device can be used to remove the MRI visibleseed(s).

Cobalt Contrast Markers

A novel contrast marker able to generate high intensity of T₁-weightedMRI signal is provided herein. This agent may be used to identifyradioactive titanium and plastic seeds in prostate brachytherapy. Thecontrast agents provided herein are based on cobalt (II)chloride-glycine compounds with basic formula (CoCl₂)_(n)(C₂H₅NO₂)_(1-n)where n=0.5-0.95, and characterize by VSM, XRD, SEM, and MRI. The aquasolution of (0.3-10%) (CoCl₂)_(0.9)(C₂H₅NO₂)_(0.1) were incorporatedinto glass and polymer capsules and were well visulalized by 1.5 T, 3 T,and 7 T MRI for quantities as low as 0.3 μL.

The ability of a T1-reducing contrast agent to generate a very brightsignal against a background of normal tissue is a function of: (a) therelaxivity and concentration of the contrast agent; (b) thecharacteristic relaxation time constants of background tissues; and (c)the acquisition parameters of the MR imaging sequence.

Following the identification of the relaxivity properties of the novelagents, we were also able to show a similar contrast betweenencapsulated markers and surrounding tissues using the cobalt complexand clinically available MRI contrast agents such as Magnevist. Incomparison to Magnevist, the relaxivity of the novel agents is lower,therefore, a higher concentration is required to achieve the T1 signalrequired.

Construction and Development of Novel Contrast Agents

The contrast marker 10 includes contrast agent 20 that are metalcomplexes such as [(CoCl₂)_(0.8)(C₂H₅NO₂)_(0.2) and L-PG-Bz-DTPA-Gd.Certain contrast agents 20 have been constructed and are found useful anMRI-visible contrast marker 10 with a high signal intensity on MRI. FIG.2 shows the structures of the compound [Co(C₂H₅NO₂)₂(H₂O)₂Cl₂]_(n) andL-PG-Bz-DTPA-Gd (average molecular weight 101,000). To develop thesecontrast agents 20, numerous agents were explored with paramagnetic,superparamagnetic, and weak ferromagnetic properties.

Contrast agents suitable for this invention include OMNISCAN™ (GEHealthcare, UK), OptiMARK, Magnevist, ProHance, and MultiHance FERIDEXI.V.® (Advanced Magnetics, Inc., Cambridge, Mass.), and colloidalnanoparticle solutions of CoFe₂O₄, Mn—Zn, Ni—Zn-ferrites, cobaltchloride, Fe—Co complex chloride, and cobalt (II) chloride-glycinecompound with different concentrations.

The cobalt-glycine complexes such as [C₂H₅NO₂]CoCl₂.2H₂O and[Co(C₂H₅NO₂)₂(H₂O)₂Cl₂]_(n) have been studied. Stenzel, K., et al., Poly[[[diaquacobalt(II)]-di-μ-glycine]dichloride], Acta Crystallographica,2004, 60(10):m1470-m72; Clegg, W., et al., Structure of ThreeGlycine-bridged Polymeric Complexes: [Mn(glycine)(H2O)2Cl2],[Co(glycine)(H2O)2Cl2] and [Co(glycine)(H2O)4](NO3)2. ActaCrystallographica, 1987, C43:794-97. The main structural feature ofcompound [Co(C₂H₅NO₂)₂(H₂O)₂Cl₂]_(n) is the coordination polyhedron ofthe Co atom on a center of inversion (FIG. 2 a). MRI contrast agent 20based on the Co²⁺ ions were prepared using anhydrous cobalt (II)chloride and glycine reactants with stoichiometry of compound(CoCl₂)_(0.8)(C₂H₅NO₂)_(0.2). The reactants were dissolved in deionizedwater and stirred at the temperature of 60° C. with a magnetic stir bar.The crystals of the (CoCl₂)_(0.8)(C₂H₅NO₂)_(0.2), compounds weresynthesized by slow water evaporation. To verify product homogeneitypurity and magnetic ordering the products were characterized using XRDand SEM microprobe analysis. Water solutions (1-10 wt. %) with differentcobalt (II) chlorides/glycine ratios were prepared for MRI testing.

Synthesis of the Cobalt Based Compounds

Co²⁺-based compounds were prepared using anhydrous cobalt (II) chloride(CoCl₂) and of amino acid-glycine (H₂N(CH₂)CO₂H) precursors. Theprecursors were purchased from Sigma Aldrich with purity (99+) and wereused as received without further purification. The ratio among thereactants was set in the following stoichiometry of compound(CoCl₂)_(n)(C₂H₅NO₂)_(1-n) where n=0.5-0.95.

Method 1. The (1.94-1.26 g) of cobalt chloride CoCl₂ (14.95-9.76 mmol)was added to 20 mL of double distillated water in a 100 mL Erlenmeyerflask, the solution was purple. Then, (0.732-0.059 g) of glycine(9.76-0.78 mmol) was dissolved in 10 mL of water in 50 mL flask. Thecobalt chloride solution was added to the amino acid solution over aone-minute period. The mixture solution was stirred for the 30 minutesat 50 C. After slow evaporation of the solution for two days, palepurple rectangular crystals were obtained.

Method 2. The reactants (1.94-1.26 g) of CoCl₂ and (0.732-0.059 g) ofglycine [H₂N(CH₂)CO₂H] were mixed and heated up to 160° C. in thenitrogen environment during 1 h. The synthesis yielded crystals ofcompound up to 5 mm.

Materials Characterization

The composition and crystal structure of the products were determined byX-ray diffraction (Siemens D5000 diffractometer) with Cu K_(α) radiation(λ=1.54056 Å).

The particle morphological features and microprobe analysis weredetermined by scanning electron microscopy (SEM; JEOL JAX8600, Japan) ofloose powder fixed to a graphite disk. The sample was sputtered bygraphite to enhance surface conductivity.

Analysis was performed using a Perkin Elmer 1600 Spectrometer with KBrbeamsplitter, and MCT detector. The resolution was 4 cm⁻¹, with 64co-added scans for the single-beam background and sample spectra. Thespectral range was from 4000-400 cm⁻¹.

Raman scattering spectra of as-synthesized solid samples were measuredat room temperature using HR640 spectrometer equipped with a microscope,notch filters, and a liquid-nitrogen-cooled CCD detector. The 488 nmlaser line, focused with a ×50 objective on a spot of (˜5 μm) diameteron the sample surface, were used for excitation.

Viscosity of contrast agent solution was measured at room temperature byusing Brookfield digital viscometer DV-II.

The Fisher 21 tensiometer was used to measure surface tension ofcontrast agents with accuracy t within +/−0.25%.

Octanol-water partition coefficients (P_(oct/wat)) were measured bydissolving 10 mg of each compound in one milliliter of a 1:1 mixture ofoctanol and water. The resulting biphasic solution was shaken vigorouslyfor two hours at which point 400 μL of the octanol layer and 400 μL ofthe water layer were removed. The solvent from each sample was removedunder reduced pressure and the mass of the compound in the octanolsample was divided by the mass of the compound in the water sample. Thisexperiment was repeated in triplicate, and the results were averaged togive the Log (P_(oct/wat)) values. All complexes were completely solublein the mixture of octanol and water.

Magnetic Characterization

Superconducting Quantum Interference Device (SQUID): Magnetic propertiesof the Co-based compounds, such as saturation magnetization, blockingtemperature, coercivity, remanence, and initial permeability weremeasured in a Quantum Design MPMS SQUID magnetometer over a broad rangeof temperatures (5 to 300K and magnetic field up to 5 Tesla). In orderto eliminate the interaction of the particles in the samples, the powderwas dispersed in paraffin.

The magnetic properties of contrast agent solutions were determined byVSM (Vibrating Sample Magnetometer) at room temperature and magneticfield up to 1.5 T.

Structure and Properties of Co/Glycine Compounds:

X-ray patterns of an as-synthesized sample produced by using method 1(with precursors containing 9.76 mmol of CoCl₂ and 0.78 mmol of glycine)(FIG. 15 a) showed that the product has an almost amorphous structure,and no reflection picks were recorded. However, after further annealingat a temperature of 80° C., a fully crystalline structure appeared. Themorphology of the annealed product is shown in FIG. 15 b. As expected,the powder is crystalline with broad particle sizes from 0.3 to 3 μm.

The Fourier Transform Infrared (FTIR) spectrum of the annealed sample isshown in FIG. 16 a. The Raman Infrared spectra of the cobalt complexidentifying its unique chemical fingerprint is shown in FIG. 16 b. Byinterpreting the infrared absorption spectrum, the chemical bonds in amolecule can be determined FTIR spectra of pure compounds are generallyso unique that they are like a molecular “fingerprint”. While organiccompounds have very rich, detailed spectra, inorganic compounds areusually much simpler.

Magnetic Properties of Solid Compounds

As shown in FIG. 17, the magnetization M(H) plot at 300K of theas-synthesized and annealed samples (FIG. 17) indicate a paramagneticproperties.

The temperature dependence of the magnetization of the annealed □sampleand hysteresis loop (measured at 5K) are shown in FIG. 18. Themeasurements show the antiferomagnetic behavior at the temperature lessthan 23K and calculation of the effective magnetic moment by Curie-Weissapproach confirmed P_(eff)=4.34 MB. The hysteresis loop confirms themetamagnetic transition from paramagnetic to antiferromagnetic at lowmagnetic field.

Contrast Agent Properties

For preparation of aqua solution of contrast agent, the as-synthesizedcobalt/glycine crystallites were dissolved in distillated water (0.3-10wt %) and stirred at the room temperature with a magnetic stir bar for 1h and then sonicated for 30 min.

FIG. 19 shows the pH value of aqua solution of various contrast agentswith concentrations from 0.3 to 10%. The value of pH varied from 2.6 to6.5.

FIG. 20 a-20 d show the magnetic properties of various aqua solutions ofCo/glycine with concentration 1, 3, 5, 8 and 10%. An increasing theconcentration of Co-based compound increased the paramagnetic behaviour.

The table below summarizes the basic properties of Co-based contrastagents.

Contrast agent Surface Partition solutions, Magnetic Viscosity, tension,Coefficient, % properties cP dynes/cm pH Log P 0.5 paramagnetic 1.0 72.86.1 (−0.15)-(−0.09) 5 paramagnetic 1.1 73.6 3.2

Encapsulated Contrast Agent Marker (ECAM)/Contrast Marker Fabrication

The Co-based solutions were filtrated through a micro-membrane filter toremove any impurities and injected into the custom design glasscapillary tube (FIG. 21 a) with the volume of contrast agent of 0.3-2μL, respectively. Several combinations of glass seeds containingcontrast agent were assembled with titanium seeds by using high-strengthwaterproof polyurethane based adhesive. FIG. 21 b shows schematicdiagram of assembled strand with ECAM and titanium seeds.

MR Imaging of the Cobalt Complex at Low and High Magnetic Fields

MRI served two roles. First, the cobalt complex (C4) was imagedquantitatively in order to establish relaxation parameters whichfacilitate quantitative simulation, protocol optimization and theability to compare the complex with other relaxation agents. The secondrole was qualitative visualization of the complex in seed or strandprototypes.

Quantitative Analysis of the C4 Complex

MR imaging measurements were performed on a 1.5 T clinical scanner(Excite HD, GEHT, Waukesha, Wis.) to characterize the relaxationproperties of the new cobalt complex after each new modification of theC4 chemistry was made. Several iterations were performed beforeobtaining a stable sample. Additional measurements at 3.0 T (Excite HD,GEHT, Waukesha, Wis.) were made once the design of the C4 complex wasstable. Each session or iteration (n=5) took approximately 2 hours tocollect all the relaxation data.

Concentrations of the complex were prepared in 0.1%, 0.3%, 0.5%, 0.75%and 1.0% solutions provided by the UH group. Theses solutions wereplaced in a water bath and imaged at room temperature (23° C.).Experiments were performed to ascertain the spin-lattice relaxivity(R1), spin-spin relaxivity (R2) and true spin-spin relaxivity (R2*) at1.5 T and 3 T using a volume knee coil to excite and receive the MRsignal.

R1 measurements were performed using a spin-echo inversion recovery(SE-IR) sequence with parameters: Inversion Time (TI)={0.05, 0.1, 0.2,0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0} sec,Pulse Repetition Time (TR)=5000, Time to Echo (TE)=10 ms, slicethickness=3 mm, acquisition matrix=256 (frequency)×128 (phase), receiverbandwidth (rBW)=±15 kHz and the number of excitations (NEX)=1.

R2 measurements were carried out using an SE sequence with parameters:TE={15, 20, 40, 60, 100, 150, 200, 250, 300 and 500 ms}, TR=5000 ms,slice thickness=3 mm, matrix size=256×128, rBW=±15 kHz and NEX=1.

R2* measurements were carried out using a multi-echo fast gradientrecalled echo (fGRE) sequence with parameters: TR=600 ms, TE varied from2.2 to 5.7 ms with an echo spacing of 3.3 ms (16 echoes), slicethickness=3 mm, matrix size=256×128, rBW=±15 kHz and NEX=1.

FIG. 22 a shows the arrangement of the different concentrations ofcobalt complex in a water phantom. Relaxation times were inverted toobtain R1, R2 and R2* measurements. These measurements displayed alinear relationship with cobalt concentration as expected (FIGS. 22 b-22d).

FIG. 23 shows the results of two R1 measurements of the cobalt complextaken 54 days apart. The idea was to see if there was any degradation orbreakdown in the complex over time however no statistically significantdifference was observed.

The slopes of R1 and R2 curve versus concentration were used todetermine the relaxivity (r1 and r2) in mM⁻¹s⁻¹ as shown in thefollowing tables. A weighted least-linear squares fitting routine waswritten in MATLAB to calculate the fit parameters accounting for theuncertainty as well as calculating the net uncertainty in the derivedmeasurement. Note that in the final quantitative analysis, R2*measurements are excluded since the samples seemed to have interferingmagnetic effects that could alter results.

TABLE 1 Measured relaxation times (T1, T2) of C4 complex at 1.5T (a) and3.0T (b) Concentration T1 (ms) T2 (ms) % Wt mM μ σ μ σ (a) 0.10 8.25782.0 72.0 836.0 140.0 0.30 24.76 379.0 29.0 354.0 136.0 0.50 41.27235.0 19.0 215.0 78.0 0.75 61.90 172.0 10.0 153.0 29.0 1.00 82.53 130.023.0 120.0 12.0 (b) 0.10 8.25 866.0 28.0 530.0 29.0 0.30 24.76 432.029.0 215.0 34.0 0.50 41.27 288.0 51.0 124.0 29.0 0.75 61.90 202.0 73.0104.0 6.0 1.00 82.53 164.0 73.0 105.0 2.0

TABLE 2 Measured relaxivity (r1, r2) of C4 complex at 1.5T (a) and 3.0T(b) Slope Intercept (mM⁻¹ s⁻¹) s⁻¹ Corr. μ σ μ σ Coeff. (a) r1 0.0860.006 0.570 0.141 0.9987 r2 0.097 0.010 0.404 0.238 0.9995 r2/r1 1.1320.141 (b) r1 0.070 0.008 0.572 0.084 0.9999 r2 0.105 0.003 1.066 0.1160.9869 r2/r1 1.494 0.179

The relaxivities at 1.5 T were r1=0.086±0.006 (mM*s)⁻¹ andr2=0.097±0.010 (mM*s)⁻¹. For reference (De Bazelaire C M J, et al,Radiology, 2004), the relaxivities of Gd-DTPA at 1.5 T (23° C.) arer1=4.68±0.06 (mM*s)⁻¹ and r2=5.57±0.07 (mM*s)⁻¹ corresponding to anr2/r1=1.12±0.01 (similar to the C4 complex response in Table 2). Thesimilarity of the ratios indicates that the T2 effects on signalenhancement are similar. The discrepancy between relaxivities indicatesthat a higher concentration of C4 is required to effect the same signalenhancement. It is noted that in these measurements, r1 sensitivitydecreases at 3.0 T while r2 sensitivity does not appear to, leading tothe potential that T2 effects may need to be accounted for in protocolsat 3 T (this trend in r1 was observed in the initial measurements seenat 7 T measured by Jim Bankson as well). Obviously, as shown in the dataabove and the following phantom images of the C4 complex, theseconcentrations are easily achievable using sealed sources.

Knowing the relaxivities, simulation of the contrast against glandularprostate tissue for T1-weighted and T2-weighted sequences commonly usedin the clinic. Note the T1 enhancement in the figure below starts todecrease around 0.75% concentration due to T2 effects on the signal.

Qualitative Visualization of the C4 Complex Using MRI

Prototypes and test vessels containing the C4 complex and variousreference markers (such as Gd-DTPA) were imaged as they becameavailable. One of the earliest experiments is shown in the figure below,where the C4 enhancement is shown in agar phantom and in an ex vivosample of canine prostate using 3D FGRE and 3D FIESTA (a T2-likeweighting).

The qualitative imaging sessions have been through many iterations ofprototype devices in order to evaluate the vessel effects (content andsize) as well as to compare the C4 to gadolinium. Several samples of 0.5mm and 0.35 mm diameter were prepared with cobalt concentrations rangingfrom 0.3% to 0.75% (see FIG. 24) were created and placed in rows at asingle level inside an agar phantom. Some of these samples containedtitanium spacers which divide up the segments where the cobalt complexis kept. The phantoms containing these samples along with controlsamples containing the same concentrations of gadolinium or distilledwater were subjected to several high-resolution 3D FSE, SPGR and FIESTAscans. These scans can be arbitrarily reformatted to any plane in orderto visualize the markers. Currently we are still in the process ofevaluating different markers prototypes given to us.

FIG. 27 shows SPGR scans containing the both the cobalt complex andgadolinium phantoms. Cobalt is shown in the second of the images.

Qualitative imaging experiments show that the casing containing thecontrast agent greatly impacts our ability to see it. It is exceedinglyhard to deconvolve these results from instances where the integrity ofthe vessel was compromised prior to imaging leaving us with reducedquantities of contrast agent to image. When the casing does notinterfere with imaging, the response of the C4 complex appears to be asanticipated by the quantitative measurements.

Gd Contrast Markers

Two types of Gd-filled contrast markers 10 were created and evaluated:low-molecular-weight Gd-chelate Magnevist (DTPA-GD) and a high-molecularweight polymeric Gd-chelate. Magnevist is used routinely in the clinic.It's relaxivity is 4.1 mM⁻¹s⁻¹ at 1.5 T in phosphate-buffered saline.Unger, E. C. S. D., et al., Gadolinium-Containing Copolymeric Chelates—ANew Potential MR Contrast Agent. MAGMA, 1999, 8(3):154-62.High-molecular-weight polymeric Gd chelates generally have increasedrotational correlation time, and hence, increased relaxivity pergadolinium atom. Applicant has synthesized and characterized Gd-chelatedpolymeric MRI contrast agent 20 based on biodegradable, biocompatiblepoly(L-glutamic acid) (L-PG) backbone. Wen, X., et al., Synthesis andCharacterization of Poly(L-Glutamic Acid) Gadolinium Chelate: A NewBiodegradable MRI Contrast Agent, Bioconjugate Chemistry, 2004,15(6):1408-15. To prepare the prototype contrast marker 10 containingL-PG-Bz-DTPA-Gd, one can crosslink L-PG-Bz-DTPA-Gd solution in situ togenerate a hydrogel in a capsule. This can be achieved by mixing aqueoussolution of L-PG-Bz-DTPA-Gd with a difunctional crosslinker such ashexane diamine and a water soluble carbodiimide as a coupling agent.Previous experiments have shown that L-PG-Bz-DTPA-Gd could readily formhydrogel in the presence of a crosslinker. The crosslink density can bevaried by varying the molar ratio of L-PG-Bz-DTPA-Gd to the crosslinker.

A Gd-chelated polymeric MRI contrast agent 20 (Gd Hydrogel) based on abiodegradable, biocompatible poly(L-glutamic acid) (L-PG) backbone wasalso synthesized and characterized. The resulting polymer,L-PG-Bz-DTPA-Gd, synthesized directly from L-PG and monofunctionalp-aminobenzyl-DTPA(acetic acid-t-butyl ester), exhibited T₁ relaxivityof 25 mM⁻¹s⁻¹ at 1.5 T, which was more than 6 times greater than that ofGd-DTPA. FIG. 3 b illustrates the positive contrast at lowconcentrations in a polymer casing 15, but negative contrast at higherconcentrations due to T2* effects. “Blooming” occurs with MR imagingwhen the contrast agent 20 is encapsulated by titanium and cannot bevisualized due to the susceptibility artifacts.

To characterize the contrast agents 20, they were filtrated and injectedinto the glass capillary tube with 4 mm in length and OD=0.8 mm, ID=0.5mm with volume of 0.5-1 μL. Water-proton relaxivities were measured atvariable temperature (278-335K), and as a function of magnetic field(1.5 T, 3 T, 4.7 T, and 7 T). Slight differences between therelaxivities of these agents at different field strengths will requireslightly different concentrations for optimal visibility at these fieldstrengths. By pH dependency of the proton relaxivities we will evaluatethe synthesized CAM for pH-responsive MRI contrast agent 20applications. Although 4.7 T is not a field strength commonly associatedwith clinical MRI, it complements the data collected at more clinicallyrelevant field strengths and helps to identify trends in agentrelaxivity.

Acrylic and glass hollow contrast markers 10 containing 2-5 μL of the(CoCl₂)_(0.8)(C₂H₅NO₂)_(0.2) aqueous solution (10-1 wt. %) were wellvisualized with a relative signal intensity ranging from 10751 to 32767in a phantom under 1.5-T MRI (T₁). The various combinations of[plastic/glass]-titanium-[plastic/glass] andtitanium-[plastic/glass]-titanium rows of therapy seeds 35 werevisualized in a dog prostate, and calculations verified the distance tothe center of the titanium therapy seeds 35 (FIG. 4). Both novel and FDAapproved Gd-based agents are shown herein as successfully incorporatedinside and around polymers such as PEEK and PMMA to achieve highpositive contrast signals. Likewise, C4 contrast agent and FDA approvedGd-based agents have been incorporated both inside and around polymersand achieved high positive contrast signals.

Characterization of the C4 Complex at 7 T Methods

Samples of the cobalt complex with concentrations of 0 mM, 8.25 mM,24.76 mM, 41.27 mM, 61.9 mM, and 85.23 mM were transferred into NMRsample tubes, immersed in relaxed water, and scanned at 7 T using aBiospec USR30/70 small animal NMR/MRI system. Characteristic T1, T2, andT2* relaxation times of the preparations were measured at eachconcentration. T1 measurements were made using a fast spin-echosaturation-recovery sequence (TE=63 ms; TR=400 ms, 500 ms, 1000 ms, 1500ms, 2500 ms, 500 ms; FOV=3.2 cm×3.2 cm; matrix=64×64; echo trainlength=12; slice thickness=1 mm) T2 measurements were made using a CPMGmulti-spin-echo sequence (TE=n×15 ms, 1≦n≦24; TR=1100 ms). T2*measurements were made using a multi-gradient echo sequence (TE=1.5ms+n×3.25 ns, 0≦n≦15; TR=500 ms, 4000 ms). The image matrix and sliceprescription for all measurements were kept constant. The characteristicT1, T2, and T2* relaxation time constants of each compartment weremeasured using Paravision 4.0., and the relaxivities of the contrastagent were estimated by fitting measured data to theSolomon-Bloembergen-Morgan model using Matlab.

Results

Representative images can be seen in FIG. 28, where the leastconcentrated preparation is in the compartment closest to the bottom ofthe image, and concentrations increase in a counterclockwise fashion.Linear regression of T1 measurements to the relaxation model can be seenin FIG. 29, while Table 1 lists the characteristic relaxation timesmeasured for each sample, along with the T1, T2, and T2* relaxivityestimates. The T1 relaxivity of the cobalt complex was measured to be0.0979 (mM·s)⁻¹, while its T2 and T2* relaxivities were measured to be0.502 (mM·s)⁻¹ and ˜0.618 (mM·s)⁻¹, respectively. For reference, the T1relaxivity of Magnevist is approximately 5.3 (mM·s)⁻¹ at 7 T. Magnevistis a FDA-approved T1-reducing MRI contrast agent that is widely used inclinical practice.

The ability of a T1-reducing contrast agent to generate a very brightsignal against a background of normal tissue is a function of therelaxivity and concentration of the contrast agent, the characteristicrelaxation time constants of background tissues, and the acquisitionparameters of the MR imaging sequence. The same contrast betweenencapsulated markers and surrounding tissue can be achieved using thecobalt complex or clinically available agents such as Magnevist, butbecause the relaxivity of the cobalt complex is lower, a higherconcentration will be required. A concentration-dependent chemical shiftwas observed in cobalt complex samples that may cause varying degrees ofimage misregistration, depending on the concentration of the agent andon the acquisition parameters of the MR imaging sequence.

TABLE 3 Concentration (mM) T2 T1 T2* T2*-2 0 120.85 2118.485 120.89388.77 8.25 74.85 980.805 141.415 146.68 24.76 45.175 524.66 50.4252.755 41.27 31.14 533.955 32.37 34.135 61.9 22.96 160.45 24.85 25.5582.53 20.84 116.5 17.99 17.64 R2 = 0.5023 R1 = 0.0979 R2* = 0.5939 R2* =0.6429 R2/R1 = 5.13 Rsquare = 0.9831 Rsquare = 0.9027 Rsquare = 0.9865Rsquare = 0.9944

Contrast agents have been traditionally characterized by theirrelaxivities. The model that defines the relaxivities (slope of linearregression curve) is the Solomon-Bloembergen-Morgan model. This modelgives the formula y=mx+b, and the relaxivity is defined as ‘m’ or theslope of the curve. The y axis is R (1/T) and the x axis isconcentration. In other words, the y axus is ‘R’ defined as therelaxation rate (ms⁻¹) which is the inverse of ‘T’ which is therelaxation time (ms). The C4 relaxivities (r1 and r2) were determined,and the relaxivity ratios were calculated at 1.5 T, 3 T, and 7 T (1.132,1.494, 5.13, respectively The C4 relaxivity ratios were very similar toGd relaxivity ratios (1.5 T=1.12, and 7 T=5.13) So, using the Gd modely=m×+b, the concentration range of Gd was optimized.

Therefore, a certain concentration range for C4 that had positivecontrast. This range in concentration for Cobalt was 0.1%-8.25 mM whichcorresponds to a T1 relaxation time of 782 ms, and 10%-825 mM whichcorresponds to a T1 relaxation time of 61 ms. By taking theconcentrations which are consistent with similar relaxation times (T1)or relaxation rates (R1=1/T1) for Gd or any other contrast agents, wecan use this methodology to calculate concentrations that providesimilar signal intensity.

EXAMPLES

The following examples are related to the novel contrast agent C4.

Example 1

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Poly(methyl methacrylate), (PMMA) andcontrast agent C4.

The C4 water solution with concentration of 0.75% was filtrated througha micro-membrane filter to remove any impurities and injected into thePMMA capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.3 mm and length,(1)=3 mm. The PMMA tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal (see FIG. 34).

Example 2

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Poly(methyl methacrylate), (PMMA) andcontrast agent C4.

The C4 water solution with concentration of 0.3% was filtrated through amicro-membrane filter to remove any impurities and injected into thePMMA capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4 mm. The PMMA tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 3

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Polyetheretherketon, (PEEK) and contrastagent C4.

The C4 water solution with concentration of 0.75% was filtrated througha micro-membrane filter to remove any impurities and injected into thePEEK capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=3 mm. The PEEK tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows good positiveMRI signal.

Example 4

This example serves to illustrate fabrication of novel MRI visiblemarker by using glass and contrast agent C4.

The C4 water solution with concentration of 0.15% was filtrated througha micro-membrane filter to remove any impurities and injected into theglass capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=3 mm. The PEEK tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 5

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Poly(methyl methacrylate), (PMMA) andcontrast agent C4.

The C4 water solution with concentration of 0.5% was filtrated through amicro-membrane filter to remove any impurities and injected into thePMMA capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4.5 mm. The PMMA tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 6

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Polyetheretherketon, (PEEK) and contrastagent C4.

The C4 water solution with concentration of 0.5% was filtrated through amicro-membrane filter to remove any impurities and injected into thePEEK capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4.5 mm. The PEEK tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 7

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Polyetheretherketon, (PEEK) and contrastagent Magnevist.

Magnevist was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePEEK capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4.5 mm. The PEEK tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 8

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Poly(methyl methacrylate), (PMMA) andcontrast agent Magnevist.

Magnevist was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePMMA capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4.5 mm. The PMMA tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 9

This example serves to illustrate fabrication of novel MRI visiblemarker by using Polytetrafluoroethylene, (PTFE) or Teflon and contrastagent C4.

The C4 water solution with concentration of 1.0% was filtrated through amicro-membrane filter to remove any impurities and injected into thePMMA capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4.5 mm. The PTFE tap was fastened to the capillary end to preventleakage of the contrast agent. Fabricated marker was placed inside theagarose phantom and tested by clinical 1.5 T MRI. The result showsexcellent positive MRI signal.

Example 10

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Poly(methyl methacrylate), (PMMA) andcontrast agent OptiMark.

OptiMark was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePMMA capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=4.5 mm. The PMMA tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows good positiveMRI signal.

Example 11

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Polyetheretherketon, (PEEK) and contrastagent ProHance.

ProHance was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePEEK capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=5.5 mm. The PEEK tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows good positiveMRI signal.

Example 12

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Polyetheretherketon, (PEEK) and contrastagent MultiHance.

MultiHance was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePEEK capillary closed with one side. The dimensions of capillary are:outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm and length,(1)=5.5 mm. The PEEK tap was fastened to the capillary end and locallyheated by laser beam to secure the conjunction and to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows good positiveMRI signal.

Example 13

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Polypropylene and contrast agent C4.

The C4 water solution with concentration of 0.3% was filtrated through amicro-membrane filter to remove any impurities and injected into thepolypropylene capillary closed with one side. The dimensions ofcapillary are: outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6mm and length, (1)=4.5 mm. The polypropylene tap was fastened to thecapillary end to prevent leakage of the contrast agent. Fabricatedmarker was placed inside the agarose phantom and tested by clinical 1.5T MRI. The result shows excellent positive MRI signal.

Example 14

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible Polyethylene and contrast agent Magnevist.

Magnevist was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePolyethylene capillary closed with one side. The dimensions of capillaryare: outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.6 mm andlength, (1)=4.5 mm. The Polyethylene tap was fastened to the capillaryend and locally heated by laser beam to secure the conjunction and toprevent leakage of the contrast agent. Fabricated marker was placedinside the agarose phantom and tested by clinical 1.5 T MRI. The resultshows excellent positive MRI signal.

Example 15

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Polyamides and contrast agent C4.

The C4 water solution with concentration of 0.3% was filtrated through amicro-membrane filter to remove any impurities and injected into thePolyamides capillary closed with one side. The dimensions of capillaryare: outside diameter, (OD)=0.7 mm, inside diameter, (ID)=0.5 mm andlength, (1)=4 mm. The Polyamides tap was fastened to the capillary endto prevent leakage of the contrast agent. Fabricated marker was placedinside the agarose phantom and tested by clinical 1.5 T MRI. The resultshows excellent positive MRI signal.

Example 16

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Polyester and contrast agent C4.

The C4 water solution with concentration of 0.75% was filtrated througha micro-membrane filter to remove any impurities and injected into thePolyester capillary closed with one side. The dimensions of capillaryare: outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.3 mm andlength, (1)=3 mm. The Polyester tap was fastened to the capillary end toprevent leakage of the contrast agent. Fabricated marker was placedinside the agarose phantom and tested by clinical 1.5 T MRI. The resultshows excellent positive MRI signal.

Example 17

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Polyurethanes and contrast agent C4.

The C4 water solution with concentration of 0.5% was filtrated through amicro-membrane filter to remove any impurities and injected into thePolyurethanes capillary closed with one side. The dimensions ofcapillary are: outside diameter, (OD)=0.8 mm, inside diameter, (ID)=0.3mm and length, (1)=4.5 mm. The Polyurethanes tap was fastened to thecapillary end to prevent leakage of the contrast agent. Fabricatedmarker was placed inside the agarose phantom and tested by clinical 1.5T MRI. The result shows excellent positive MRI signal.

Example 18

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Polyvinylchloride and contrast agentC4.

The C4 water solution with concentration of 0.5% was filtrated through amicro-membrane filter to remove any impurities and injected into thePolyvinylchloride capillary closed with one side. The dimensions ofcapillary are: outside diameter, (OD)=0.7 mm, inside diameter, (ID)=0.5mm and length, (1)=4 mm. The Polyvinylchloride tap was fastened to thecapillary end to prevent leakage of the contrast agent. Fabricatedmarker was placed inside the agarose phantom and tested by clinical 1.5T MRI. The result shows excellent positive MRI signal.

Example 19

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Polyvinylchloride and contrast agentMagnevist.

Magnevist was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into thePolyvinylchloride capillary closed with one side. The dimensions ofcapillary are: outside diameter, (OD)=0.7 mm, inside diameter, (ID)=0.5mm and length, (1)=4 mm. The Polyvinylchloride tap was fastened to thecapillary end to prevent leakage of the contrast agent. Fabricatedmarker was placed inside the agarose phantom and tested by clinical 1.5T MRI. The result shows excellent positive MRI signal.

Example 20

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade polyglycolic acid, (PGA) andcontrast agent C4.

The C4 water solution with concentration of 0.5% was filtrated through amicro-membrane filter to remove any impurities and injected into the PGAcapillary closed with one side. The dimensions of capillary are: outsidediameter, (OD)=0.8 mm, inside diameter, (ID)=0.3 mm and length, (1)=3mm. The PGA tap was fastened to the capillary end to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Example 21

This example serves to illustrate fabrication of novel MRI visiblemarker by using biocompatible grade Poliglycolic acid, (PGA) andcontrast agent Magnevist.

Magnevist was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and injected into the PGAcapillary closed with one side. The dimensions of capillary are: outsidediameter, (OD)=0.8 mm, inside diameter, (ID)=0.3 mm and length, (1)=3mm. The PGA tap was fastened to the capillary end to prevent leakage ofthe contrast agent. Fabricated marker was placed inside the agarosephantom and tested by clinical 1.5 T MRI. The result shows excellentpositive MRI signal.

Summary of the examples for fabrication and testing the MRI visiblemarker are presented below in Table 4.

TABLE 4 Marker Amount of size, (mm) Contrast Contrast MRI ExamplesMarker Material OD ID agent Concentration, % agent, (μl) Visualization 1Poly(methyl 0.8 0.3 C4 0.75 0.28 excellent methacrylate), (PMMA) 2 PMMA0.8 0.6 C4 0.3 0.84 excellent 3 Polyetheretherketon, 0.8 0.3 C4 0.750.28 good (PEEK) 4 Glass 1.0 0.3 C4 0.15 0.28 excellent 5 PMMA 0.8 0.6C4 0.5 0.9 excellent 6 PEEK 0.8 0.6 C4 0.5 0.9 excellent 7 PEEK 0.8 0.6Magnevist Diluted 1/20 0.84 excellent 8 PMMA 0.8 0.6 Magnevist Diluted1/20 0.84 excellent 9 Polytetra- 0.8 0.6 C4 1.0 0.84 excellentfluoroethylene, (PTFE) 10 PMMA 0.8 0.6 OptiMark Diluted 1/20 0.84 good11 PEEK 0.8 0.6 ProHance Diluted 1/20 1.13 good 12 PEEK 0.8 0.6MultiHance Diluted 1/20 1.13 good 13 Polypropylene 0.8 0.6 C4 0.3 0.84excellent 14 Polyethylene 0.8 0.6 Magnevist Diluted 1/20 0.84 excellent15 Polyamides 0.7 0.5 C4 0.3 0.56 excellent 16 Polyester 0.8 0.3 C4 0.750.28 excellent 17 Polyurethanes 0.8 0.6 C4 0.5 0.84 excellent 18Polyvinylchloride 0.7 0.5 C4 0.5 0.56 excellent 19 Polyvinylchloride 0.70.5 Magnevist Diluted 1/20 0.56 excellent 20 Polyglycolic acid, 0.8 0.3C4 0.5 0.28 excellent (PGA) 21 Polyglycolic acid, 0.8 0.3 MagnevistDiluted 1/20 0.28 excellent (PGA)

Example 22

This example serves to illustrate integration of novel MRI visiblemarker (fabricated as described in Example 2) next to the titanium seedsby using standard biodegradable (polyglycolic acid) brachytherapystrand. FIG. 6 shows the schematic diagram of a loaded strand withtitanium seeds and MRI visible markers. FIG. 35 a shows the photographof the fabricated brachytherapy strand: MRI visible markers wereintegrated with dummy titanium seeds. FIG. 35 b shows that MRI visiblemarkers permit positive MRI identification of titanium seeds inbrachytherapy strand.

Example 23

This example serves to illustrate fabrication of novel MRI visiblemarker by using an absorptive fiber (cotton rope), contrast agent C4 andbiocompatible Poly(methyl methacrylate)-(PMMA) polymer dissolved indichloromethane.

The C4 water solution with concentration of 0.5% was filtrated through amicro-membrane filter to remove any impurities and impregnated into theabsorptive fiber. The dimensions of fiber are: outside diameter,(OD)=0.6 mm and length, (1)=20 mm. After saturation of C4 agent into theabsorptive fiber, fiber was coated by polymer(25%-PMMA/85%-dichloromethane) solution. The polymer solution wasentrapped after the overcoating is dry. The thickness of the coating maybe regulated by number of fiber immersion into the polymer solution. Inour experiment the final OD of the fiber with polymer coat was 0.8 mm.Fabricated marker was placed inside the agarose phantom and tested byclinical 1.5 T MRI. The result shows good positive MRI signal.

Example 24

This example serves to illustrate fabrication of novel MRI visiblemarker by using an absorptive fiber (cotton rope), contrast agentMagnevist and biocompatible Poly(methyl methacrylate)-(PMMA) polymerdissolved in dichloromethane.

Magnevist was diluted in water with ratio 1/20 and filtrated through amicro-membrane filter to remove any impurities and impregnated into theabsorptive fiber. The dimensions of fiber are: outside diameter,(OD)=0.6 mm and length, (1)=20 mm. After saturation of contrast agentinto the absorptive fiber, fiber was coated by polymer(25%-PMMA/85%-dichloromethane) solution. The polymer solution wasentrapped after the overcoating is dry. The thickness of the coating maybe regulated by number of fiber immersion into the polymer solution. Inour experiment the final OD of the fiber with polymer coat was 0.8 mm.Fabricated marker was placed inside the agarose phantom and tested byclinical 1.5 T MRI. The result shows good positive MRI signal. FIG. 36shows the MRI image of the ECAM fabricated by using absorptive fiber,magnevist and PMMA/dichloromethane solution.

Another Prophetic Example for In Vitro Evaluation

Contrast markers 10 can be implanted into a prostate phantom to test theimaging performance of a contrast marker 10, and optimize MRI-baseddosimetric evaluation of the prostate and surrounding critical organstructures in vitro. To test the performance of the contrast marker 10with respect to facilitating MRI-based dosimetric evaluation of atumor-bearing canine prostate and critical organ structures in vivo apilot study of MRI perfusion, diffusion, and spectroscopy with thecontrast marker 10 can be conducted. One can determine, in alarge-animal in vivo model of cancer, whether the contrast marker 10permits the use of functional MRI to enhance the delivery and dosimetricevaluation of prostate brachytherapy.

To test the performance of the contrast marker 10 with respect tofacilitating MRI-based dosimetric evaluation of the prostate andcritical organ structures in a prostate, the strand 30 containingnon-radioactive titanium seeds (functioning as spacer elements 45) arepreloaded along with contrast markers 10 and the strand 30 implantedinto the prostate phantom. Optimization of MRI-based dosimetry of theprostate and surrounding critical organ structures can be performed.Dosimetry can be evaluated using an arbitrary fixed activity andprostate dose prescription for dosimetric calculations.

In order to conduct preliminary testing of the system, one can use adisposable prostate phantom (Model M53F, Computerized Imaging ReferenceSystem, Inc., Norfolk, Va.), shown in FIG. 7. The phantom contains aliquid medium surrounding a Zerdine™ water-based polymer gel prostateand a penetrable “perineum” for catheter insertion. Though intended forultrasound imaging, the phantom components are CT and MR-compatible andare easily visualized on CT and MR images. The positional grid templateroutinely used in clinical prostate brachytherapy can be affixed to thefront of the phantom for positional measurements. The strand 30containing the non-radioactive seeds (spacer elements 45) with contrastmarkers 10 will be positioned accurately within this grid at any one ofthe grid locations.

An ultrasound Endo-PII probe (Model G20, Sonoline, Siemens MedicalSystems, Mount View, Calif.) can be inserted into the rectal opening inthe phantom and ultrasound images can be captured every 5 mm within thephantom. Images are typically taken from the base to the apex of theprostate. The output screen has an electronic grid superimposed on allthe images to simulate the locations of the needle i.e the strand 30insertions. These captured images can then be transferred to theprostate brachytherapy treatment planning system Variseed 7.2. (VarianMedical Systems, Charlottesville, Va.). The organ structures within thephantom can be contoured. Multiple treatment-plans can be generatedbased on various predetermined geometries of the therapy seeds 35. Basedon an assumed activity of each therapy seed 35 to be 1 mCi, dosedistributions and dose volume histograms (DVH's) can be computed.

Based on the simulated treatment plans, the spacer elements 45 withcontrast markers 10 can be physically placed in the phantom at locationsdetermined on a given treatment plan. The phantom can be placed into astandard head coil and inserted into the bore of a 1.5 T and 3 Tsuperconducting MRI scanner (Signa, GE Medical Systems, Waukesha, Wis.).A series of images can be acquired using clinical MRI sequencingprotocols. The acquired multiple image sets can be transferred to aRadiation Oncology DICOM storage server Evercore (TeraMedica, Milwaukee,Wis.) from where they can be imported into Variseed 7.2. The prostateand organ structures within the phantom can be contoured from theacquired images. Following the identification of contrast markers 10,the location of the therapy seeds 35 can be determined and dose computedfor each treatment plan.

To illustrate the ability to identify therapy seeds 35 using contrastmarkers 10, non-radioactive seeds (spacer elements 45) without contrastmarkers 10 can be implanted into a separate prostate phantom. The seedscan be implanted into identical coordinates as the phantom with contrastmarkers 10. MR imaging data sets of the phantoms with and withoutcontrast markers 10 can then be qualitatively compared.

In order to illustrate the superiority of MR-based dosimetry usingcontrast markers 10 over CT-based dosimetry, qualitative comparisonsbetween MR- and CT-based dosimetry can be performed. Using a GEmulti-slice CT scanner (GE Medical Systems, Pewaukee, Wis.), a CT dataset of the identical phantom can be obtained. Following transfer of theCT data sets to Variseed 7.2, the prostate and critical organ structurescan be contoured to generate CT-based dosimetry. A qualitativecomparison of MR-based dosimetry to CT-based dosimetry can be performed.

Yet Another Prophetic Example for In Vivo Evaluation

A total of 4 male mongrel dogs can be used for these studies. Twoanimals will be implanted with non-radioactive seeds (spacer elements45) with contrast markers 10 under MR guidance for the purpose ofvalidating the ability to image the seeds and obtain useful treatmentplanning in an in vivo large animal model using MRI anatomy. The othertwo animals will have transmissible venereal tumor (TVT) inoculated intothe prostate using sterile techniques (TVT source: fresh or frozentissue harvested from SCID mice in which tumors are perpetuated or fromprevious dogs). Rivera, B., et al., Canine Transmissible Venereal Tumor:A Large-Animal Transplantable Tumor Model, Comparative Medicine, 2005,55(4):335-43. These tumors can be treated using the MR visible seeds forthe purposes of investigating the ability to use MRI to follow-uptreatment with implanted therapy strands. All animal experiments will beconducted under the supervision of and in accordance with The Universityof Texas M. D. Anderson Cancer Center's Internal Animal Care and UseCommittee Guidelines.

All MR procedures can be performed on a clinical 1.5 T scanner (ExciteHD, Waukesha, Wis.) which has been used extensively for minimallyinvasive procedure development in large animal models in the past.McNichols, R. J., et al., Percutaneous MRI Guided Laser Thermal Therapyin Canine Prostate, SPIE, 2005, 5686:214; Diederich, C. J., et al.,Transurethral Ultrasound Applicators with Directional Heating Patternsfor Prostate Thermal Therapy: In Vivo Evaluation Using MagneticResonance Thermometry, Medical Physics, 2004, 31(2):405-13;Kangasaniemi, M., et al., Dynamic Gadolinium Uptake in Thermally TreatedCanine Brain Tissue and Experimental Cerebral Tumors, InvestigativeRadiology, 2003, 38(2):102-07; Kangasniemi, M., et al., Multiplanar MRTemperature-sensitive Imaging of Cerebral Thermal Treatment UsingInterstitial Ultrasound Applicators in a Canine Model, JMRI, 2002,16(5):522-31; Hazle, J. D., et al., MRI-Guided Thermal Therapy ofTransplanted Tumors in the Canine Prostate Using a DirectionalTransurethral Ultrasound Applicator, JMRI, 2002, 15(4):409-17. Animalswill be anesthetized (maintained with 1%-5% isofluorane in the MR suite)and brought into the MR suite for imaging. A 4-channel phased array coilcam be placed for imaging (GEHT, Waukesha, Wis.). An integratedendorectal probe (Model BPX-15, MedRad, Inc., Indianola, Pa.) will befilled with a liquid fluorocarbon material (Fluorinert, 3M Co, St. Paul,Minn.) in order to provide proper loading and enhance the ability toproperly shim the magnetic field.

MRI Protocols: Prior to placement of seeded strands 30, baselineT2-weighted anatomical, diffusion (single-shot fast spin-echo basedtechnique to minimize effects of titanium seeds with b=0, 500), 3Dspectroscopic images (PROSE, for non-metal seeds only), high resolution3D T1-weighted imaging (short echo-time, rf-spoiled gradient-recalledacquisition) and 3D dynamic contrast enhanced (fast rf-spoiledgradient-recalled acquisition technique with Magnevist, 0.2 ml/kg).T2-weighted images (fast spin-echo) can be used to plan the treatmentdelivery. A 3D fast-recovery fast-spin echo acquisition using parallelimaging will be investigated for providing isotropic resolutionT2-weighted images of the prostate anatomy in a reasonable amount oftime. If this sequence fails, standard 2D fast spin-echo imaging can beused (e.g., FIG. 3 a). Treatment planning images can be performed with agrid template overlay (FIG. 8) adapted to the canine prostate withcontrast markers 10 for guiding the placement of radioactive seedspercutaneously (Biotex, Inc, Houston, Tex.) which are registered to theMR coordinate system. McNichols, R. J., et al., Percutaneous MRI GuidedLaser Thermal Therapy in Canine Prostate, SPIE, 2005, 5686:214.

After seeded strand 30 placement, the prostate can be immediatelyre-imaged with MRI to evaluate the ability to locate seeds placed in theanimal prior to removing the animal from the table. CT imaging can beperformed immediately afterward in the Veterinary Research Laboratory.Both MR- and CT-data set images will be fed into the Variseed 7.2treatment planning system. In order to illustrate the superiority ofMR-based dosimetry using contrast markers 10 over CT-based dosimetry,qualitative comparisons between MR- and CT-based dosimetry can beperformed on the prostate and critical organ structures. A qualitativecomparison of MR-based dosimetry to CT-based dosimetry can be performed.Follow-up MR- and CT-imaging of the animals at 30 and 60 days willfacilitate the ability to track the seeds with contrast markers 10 afterthe prostate edema and intra-prostatic hemorrhage has resolved.

Palladium radioactive therapy seeds 35 where (Pd-103) is selected as aradioactive agent due its relatively short half-life (17 days), clinicalapplicability, and to permit evaluation of the prostate with functionalMR-imaging at 30 and 60 days after approximately 90% of the radiationdose has been delivered. Transmissible venereal tumor (TVT) isintroduced into the canine prostate because a reliable tumor model in alarge animal that closely resembles the dimensions of humans is notavailable (Rivera et al. Comparative Medicine 2005). In order to getexperimental tumors to grow in the canine prostate, each dog will beimmunosuppressed with cyclosporin (10 mg/kg per os b.i.d. for 2 weeksand then s.i.d. until the animal is sacrificed). Immunosuppressiontherapy commences 7-10 days prior to tumor inoculation.

For tumor inoculation, dogs will be anesthetized in an operating roomdedicated to, and properly equipped for, large animal operatingprocedures. One lobe of the prostate will be inoculated with TVT (0.25cc to 0.5 cc) via ventral midline laparotomy access using a 16-20 Gneedle. Tumors will be allowed to grow for 5-10 weeks to reach maximumdiameters of 10-15 mm in the prostate. All animals will be monitoreddaily for well-being and periodically palpated for tumor development andsize. Animals may be periodically (up to weekly) anesthetized and imagedduring the tumor growth period to evaluate the tumor growth and size andto obtain baseline MR images prior to therapy seed 35 implantation. MRimaging will utilize an 8-channel phased array coil. Tumor growth willbe assessed using MR-diffusion, perfusion and spectroscopic imaging(FIGS. 9-10).

When the tumor in the prostate is approximately 1.0-1.5 cm, the animalwill be prepared for seed placement. Therapy seed 35 placement andimaging will proceed in the MR environment. Baseline MR of the tumorprior to treatment, including diffusion, perfusion, dynamic contrastenhanced imaging (FIG. 9) and spectroscopy (FIG. 10) will be collectedand compared to time points at 60 and 90 days post-therapy asillustrated in. Finally, one can correlate the prostate MR functionalimaging and pathology (FIG. 11) with MRI-based dosimetry.

The ability to visualize and account for each contrast marker 10 in theseeded strand 30 placed from post-implantation 3D T1-weighted imageswill be assessed at 60 and 90 days. We will evaluate the ability tomanually locate therapy seeds 35 with Variseed 7.2 software and thetreatment plan from the 3D T1-weighted images will be assessed. Dose toanatomy and critical organ structures will be determined via a fusedT2-weighted anatomical images for manual segmentation.

The effects of non-radioactive seeds (spacer elements 45) on MR imagingquality will be assessed immediately post implantation, and at 60 and 90days. Anatomical evaluation can be performed to qualitative assessartifacts and changes in image quality. Following diffusion and dynamiccontrast enhanced imaging a qualitative assessment of artifacts andchanges in image quality due to the presence of the therapy strand.Quantitative analysis of the apparent diffusion coefficient, DCE initialarea under the curve (IAUC) and the total area under the curve (AUC)will be recorded, but it is expected that physiological changes due tothe procedure (i.e., inflammation and hemorrhage) may limit thequantitative nature of these results. Following spectroscopy, theeffects of the therapy strand will be noted by looking at the relevantcalibration parameters (primarily line width after shimming and percentwater suppression) for the sequence and the quality of the resultingspectrum (spectral resolution as well as water and lipid suppressionover the prostate volume). Results from can be tracked to observe effectof treatment of the prostate.

Preclinical studies have revealed positive contrast with 0.3-2 microliters of a solution of contrast agent 20 (FIG. 4 b). The small size ofthe contrast marker 10 with a limited (−0.5 micro liter) amount ofcontrast agent 20 may require multiple contrast markers 10 for MRIassessments. Geometric distortion can be an impediment to MR treatmentplanning, but with brachytherapy, this may be minimized do to theproximity of dose to the isocenter. Magnetic susceptibility of metallictherapy seeds 35 may degrade our ability to perform MR spectroscopy.Therefore, a plastic radioactive therapy seed 35 may be more appropriatein this environment.

Ideally, the contrast agent 20 compound is biocompatible and not harmfulto the human body. In the Toxicological Profile for Cobalt published bythe U.S. Department of Health and Human Services in 2004, cobalt isnoted to be an essential element for daily consumption and required forVitamin B12. In the event the capsule of the contrast marker 10 iscompromised there should be no cobalt induced toxicity.

This innovative MRI-based approach to prostate brachytherapy with ancontrast marker 10 will permit immediate post-operative MRI dosimetricevaluation of the quality of the implant. MRI-based dosimetry can beperformed at any center in the country with access to an MRI. If thedose delivered to the prostate cancer is less than adequate, the patientmay be taken back to the operating room and additional therapy seeds35/therapy strand 30 implanted to treat the cancer effectively. In thefuture, MRI-guided prostate brachytherapy with a contrast marker 10would facilitate intraoperative dosimetric evaluation to the prostatecancer and surrounding critical organ structures. Optimizing doseintraoperatively with MRI will ensure that each patient receives thehighest quality implant and may result in higher cure rates, decreasedside-effects, and an improvement in patients' quality of life.

The contrast marker 10 may permit accurate localization of theradioactive therapy seeds 35 with MRI both during the prostatebrachytherapy implant and on subsequent follow-up. Additionally the dataobtained by MRI will provide objective analysis to establish nationalstandards of quality for brachytherapy implants. Once the MRI-visiblecontrast marker 10 is developed, MRI-based prostate brachytherapydosimetry will be able to accurately define the dose of radiationdelivered to the prostate and surrounding critical organ structures.With accurate dose determination, cancer cure rates will increase andside-effects will decrease translating into an improvement in quality oflife. The MRI visible contrast marker 10 will permit translatableconsistent high-quality prostate brachytherapy implants using MRI-baseddosimetry. Therefore, MRI-based prostate brachytherapy dosimetry willimmediately replace CT-based dosimetry and permit the establishment ofnational standards of quality for prostate brachytherapy.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles. For example, thesecontrast markers can be used for additional applications; stents,drains, filters, balloons for minimally invasive procedures, cathetersfor both low dose rate (LDR), pulse dose rate (PDR) and high-dose rate(HDR) radiation therapy, applicators for the treatment of gynecologicmalignancies, catheters for the treatment of breast and head and neckmalignancies, fiducial markers for image guided radiation therapy,MR-guided monitoring probes of thermal therapies (i.e. laser-induced,RF-induced, and cryomediated procedures), biopsy needles, intravascularcontrast agent for MRI-guided vascular interventions, guidewires,intraprostatic contrast agent.

What is claimed is:
 1. A contrast agent comprising[(CoCl₂)_(n)(C₂H₅NO₂)_(1-n)] (where n=0.5-0.95).
 2. The contrast agentof claim 1, wherein the contrast agent is disposed within a casing of acontrast marker.
 3. The contrast agent of claim 2, wherein the casing iscoated.
 4. The contrast agent of claim 2, further comprising a carriersubstrate positioned within the casing.
 5. The contrast agent of claim2, further comprising a radioactive therapeutic agent disposed withinthe casing.
 6. The contrast agent of claim 2, wherein the contrastmarker is position with a strand.
 7. The contrast agent of claim 6,further comprising at least one therapy seed wherein the contrast markerwith the contrast agent and the therapy seed are positioned within thestrand.
 8. The contrast agent of claim 6, further comprising at leastone spacer element disposed in the strand with the contrast agent. 9.The contrast agent of claim 6, wherein a radioactive agent selected fromthe group consisting of palladium-103, iodine-125, and cesium-131 ispositioned within a strand.
 10. The contrast agent of claim 1, whereinthe contrast agent is disposed in a contrast marker and the contrastmarker is disposed in a therapy seed.
 11. The contrast agent of claim10, wherein a radioactive agent is disposed in the therapy seed.
 12. Thecontrast agent of claim 10, wherein said therapy seed is coated with thecontrast agent.
 13. A method of making a strand comprising: providing apolymer strand; attaching at least one contrast marker with the strand,wherein the contrast marker includes [(CoCl₂)_(n)(C₂H₅NO₂)_(1-n)] (wheren=0.5-0.95).
 14. The method of claim 13, further comprising attaching atleast one therapy seed with the strand.
 15. The method of claim 14,further comprising positioning a spacer element between the contrastmarker and the therapy seed.
 16. A method of making a contrast agentuseful in magnetic resonance imaging comprising the steps of:determining the T1 relaxation time of a first contrast agent comprising[(CoCl₂)_(n)(C₂H₅NO₂)_(1-n)] (where n=0.5-0.95); and providing a secondcontrast agent wherein the concentration level of the second contrastagent is adjusted so as to produce substantially similar T1 relaxationtimes for MR imaging to the first contrast agent.
 17. The method ofclaim 16, wherein the second contrast agent is a contrast agentcomprising gadolinium chelated with a multidentate ligand.